Biology 110

Study Notes Exam 2

 

Chapter 8: The Nervous System

 

Divisions of the Nervous System

-       central nervous system (CNS): brain & spinal cord

-       peripheral nervous system (PNS): cranial & spinal nerves & their branches

o      somatic nervous system

o      autonomic nervous system

 

Functions of the Nervous System

-       permits sensory input

-       performs integration

-       stimulates motor output

 

Cells of Nervous Tissue

-       neurons: primary cell of nervous tissue

o      have 3 parts:

       cell body: contains nucleus & other organelles

       dendrite(s): receive information from other neurons & conduct information to cell body

       axon: conducts nerve impulses away from cell body

o      3 types of neurons:

       motor neurons: conduct impulses from CNS to effector organs (muscles or glands)

      efferent neurons (take impulse away from CNS)

      have short dendrites & long axon

       sensory neurons: conduct impulses from peripheral body parts to CNS

      afferent neurons (take impulse toward CNS)

      begin at receptors, which are sensory nerve endings sensitive to internal & external stimuli

       interneuron: found only in CNS; conducts impulses between parts of CNS

o      fibers: dendrites & axons of neurons

o      myelin sheath: Schwann cell wrapped around fibers outside CNS

       provides electrical insulation & much faster impulse conduction

       neurilemmal sheath: cytoplasm & nucleus of Schwann cell; promotes regeneration of injured fibers

       nodes of Ranvier: gaps between adjacent Schwann cells

       multiple sclerosis (MS): chronic autoimmune disease where body's immune cells attack & destroy myelin sheath (forms hardened scars or scleroses)

-       neuroglial cells: support, protect & nourish neurons

o      PNS neuroglial cells:

       Schwann cells: form myelin sheath in PNS

o      CNS neuroglial cells:

       microglial cells: phagocytes; destroy microbes (bacteria) & clear debris

       astrocytes: form bridges between neurons & capillaries; may deliver nutrients to neurons

       oligodendroglial cells: form myelin sheath in CNS

       ependymal cells: ciliated cells that circulate cerebrospinal fluid (CSF) in ventricles (cavities) in CNS

 

Nerve Impulses:

-       inside of neuron is negative with respect to outside (due to negatively charged proteins in cell & Na+/K+ pump that pumps sodium out of cell)

-       resting potential: charge (voltage) across membrane; normally -70mV

-       depolarization: sodium flows into neuron; neuron becomes more positive inside

-       action potential: if enough sodium ions flow in, nerve cell fires or sends nerve impulse (sodium ions) along axon

-       repolarization: pump sends potassium ions out of cell to return negative resting potential

-        in myelinated fibers, nerve impulse skips from one node of Ranvier to next (faster)

 

The Synapse:

-       synapse: junction of axon of one neuron & another neuron (usually at dendrite)

o      axon membrane of first neuron is presynaptic membrane; dendrite membrane of second neuron is postsynaptic membrane

o      synaptic cleft: small gap between neurons in synapse

o      neurotransmitters: chemicals that transmit impulse across synapse

       acetyl choline (ACh): neurotransmitter used throughout nervous system

      broken down after signal reaches postsynaptic membrane by acetylcholinesterase (AChE)

       norepinephrine (NE): another common neurotransmitter

       serotonin & dopamine are neurotransmitters associated with behavior (mood, tension, learning memory)

       stimulatory neurotransmitters increase likelihood of impulse

       inhibitory neurotransmitters decrease likelihood of impulse

       Parkinson Disease is due to a deficiency of dopamine

      characterized by wide-eyed, unblinking expression, muscular rigidity & involuntary tremors

       In Huntington Disease there is a decrease in the neurotransmitter GABA

      autosomal dominant disorder due to chromosomal changes (trinucleotide repeats)

      leads to deterioration of nervous system; constant thrashing movements & eventually insanity & death

       Alzheimer disease is due to loss of neurons that use ACh as neurotransmitter

 

Nerves: cordlike organs of PNS consisting of bundles of axons enclosed in layers of connective tissue

-       sensory (afferent) nerves: carry impulses toward CNS

-       motor (efferent) nerves: carry impulses away from CNS

-       mixed nerves: contain both sensory & motor fibers (can be somatic &/or autonomic fibers)

-       white matter: myelinated fibers in CNS

-       gray matter: mostly nerve cell bodies & unmyelinated fibers in CNS

 

Reflexes & the Reflex Arc:

-       reflexes: automatic, involuntary responses to stimuli

-       control heart & breathing rate, body temperature, swallowing, sneezing, reactions to pain, etc.

-       sensory receptor: distal end of sensory neuron; responds to stimulus

-       sensory neuron: carries impulse from receptor to axon terminals in gray matter of spinal cord (or brain stem)

o      ganglia: collections of neuron cell bodies associated with nerves in PNS

o      dorsal root ganglion: cell bodies of sensory nerves entering spinal cord

-       integration center: within CNS gray matter, signal travels across synapse or through interneuron, generating a response

-       motor neuron: response impulse is sent from sensory neuron or interneuron through motor neuron to effector

-       effector: muscle or gland that carries out response (reflex)

-       stretch reflex: causes contraction of skeletal muscle in response to muscle stretching

-       tendon reflex: causes muscle relaxation in response to increasing muscle tension (to prevent tendons from tearing)

-       flexor (withdrawal) reflex: causes muscle contraction to move body region away from painful stimulus

o      plantar flexion reflex: curling under of toes in response to stimulation of lateral outer margin of toe

       damage to descending motor pathways causes great toe extension (Babiski sign), although a normal response in infants

 

Central Nervous System

Brain:

-       Brain Stem:

o      midbrain: between diencephalon & pons

       cerebral aqueduct: connects third & fourth ventricles

       corpora quadrigemina: midbrain nuclei

       contains visual , auditory & touch reflex centers

o      pons: between midbrain & medulla oblongata

       conduction tracts (pons = bridge); complete pathways between higher brain centers & spinal cord; relays between motor cortex & cerebellum

       works with medulla to regulate breathing rate

o      medulla oblongata: most inferior part of brain stem; blends with spinal cord

       tracts cross over to opposite side before entering spinal cord... cerebral hemispheres control voluntary movements of muscles on opposite side of body

       sensory & visceral motor nuclei (control heart rate & blood vessel diameter, breathing rate, vomiting, coughing...)

 

-       Diencephalon: central core of forebrain; surrounded by cerebral hemispheres

o      thalamus: most (80%) of diencephalon & forms walls of third ventricle

       central relay station: sorts & edits sensory information & relays to appropriate area of sensory cortex & association areas

       most inputs to cerebral cortex travel through thalamic nuclei (emotion, visceral & motor activity...)

o      hypothalamus: below thalamus; merges with midbrain inferiorly

       connected to pituitary gland by stalk called infundibulum

       main visceral control center; controls homeostasis

      roles: autonomic control center, center for emotional response,  body temperature regulation, regulation of food intake, regulation of water balance & thirst, regulation of sleep-wake cycles, control of endocrine system function

o      epithalamus: dorsal area of diencephalons, forms roof of third ventricle

       pineal gland: secretes hormone melatonin - helps in regulation of sleep-wake cycle

       choroid plexus: secretes CSF

 

-       Reticular Formation: extends through core of brainstem

o      reticular activating system: maintains cerebral cortical alertness

o      filters out repetitive stimuli

o      motor nuclei help regulate skeletal & visceral muscle activity

 

-       Cerebellum: dorsal to pons & medulla; inferior to occipital lobes; ~ 11% of total brain mass

o      bilaterally symmetrical with two hemispheres connected medially by vermis

o      surface gray matter & deep white matter

o      processes information from cerebral motor cortex & from sensory pathways

o      sends instructions to cerebral motor cortex & motor centers to regulate balance, posture & coordinated skeletal muscle movement

 

-       Cerebral Hemispheres:

o      superior part of brain; ~ 83% of total brain mass

o      3 regions: cerebral cortex (gray matter), white matter & basal nuclei

o      gyri: elevated ridges of brain tissue, separated by shallow grooves called sulci

o      fissures: deeper grooves separating larger regions of brain

o      deep sulci divide cerebral hemisphere into 5 lobes: frontal, parietal, temporal, occipital & insula

o      cerebral cortex: conscious mind; awareness, communication, memory & understanding & initiation of voluntary movements

       billions of neurons; ~ 40% of total brain mass

       Brodmann areas: 52 structural regions of cortex

       cortex has 3 types of functional areas:

      motor areas: control voluntary motor functions

      sensory areas: conscious awareness of sensation

      association areas: integrate information for voluntary action

       each hemisphere controls sensory & motor functions of opposite side of body

       cerebral palsy: spastic weakness of arms & legs due to damage to motor areas of cerebral cortex from a lack of oxygen during birth

       Broca's area: near base of primary motor area

      present in one hemisphere only (generally left)

      special motor speech area - controls muscles of tongue, throat & lips during (& possibly in planning of) speech

       stroke: blood supply to brain temporarily halted due to burst blood vessel or blood clot

      can damage Broca's area - often speech problems after stroke

 

-       Basal Nuclei (basal ganglia): subcortical nuclei deep within cerebral white matter

o      regulate motor control (muscle movements, & perhaps also attention & cognition)

o      amygdala: on tail of caudate nucleus; part of limbic system

 

-       Limbic System: regions of the medial aspects of each cerebral hemisphere & diencephalon encircling brain stem (limbus = ring) & linked by the fornix

o      emotional brain

o      amygdala: recognizes angry or fearful facial expressions, assesses danger & elicits fear response

o      cingulate gyrus: regulation of expression of emotions & feelings of frustration

o      hippocampus: plays a role in storing information in long-term memory

 

Spinal Cord:

Anatomy of Spinal Cord:

-       31 pairs of spinal nerves attach to spinal cord by paired roots

-       spinal nerves: communicate between spinal cord & body tissues served

       dorsal roots carry sensory tracts to spinal cord

       ventral roots send motor tracts away from spinal cord

-       central gray matter (unmyelinated fibers): anterior, posterior & lateral horns

-       outer white matter forms columns

o      ascending& descending tracts: carry nerve impulses through CNS

Functions:

-       center for thousands of reflex arcs using spinal nerves

-       communication between brain & PNS

 

Meninges & Cerebrospinal Fluid (CSF)

-       meninges: 3 connective tissue membranes just external to spinal cord (& brain)

o      dura mater: outer layer

o      arachnoid: middle layer; subarachnoid space contains large capillaries & CSF

o      pia mater: innermost layer; just superficial to spinal cord

-       cerebrospinal fluid: formed by choroid plexuses hanging from the roof of the ventricles in the brain

o      within ventricles of brain & central canal of spinal cord

o      supplies CNS with nutrients from blood & returns wastes to blood

Peripheral Nervous System (PNS)

Somatic Nervous System: includes all nerves that serve the musculoskeletal system & exterior sense organs (skin)

-       exterior sense organs bear sensory receptors that receive external stimuli & send impulses to CNS

-       CNS response is sent through motor neurons to effectors (skeletal muscles)

 

Cranial Nerves: know names, #'s & basic functions

 

Spinal Nerves: 31 pairs

-       8 pairs of cervical; 12 pairs of thoracic; 5 pairs of lumbar ; 5 pairs of sacral; 1 pair of coccygeal

 

Autonomic Nervous System: motor neurons that innervate smooth muscle, cardiac muscle & glands

-       also known as the involuntary nervous system (subconscious control) & the general visceral motor system

-       for each impulse there is 1 autonomic ganglion & 2 motor neurons

-       first motor neuron has cell body in CNS & preganglionic fiber

-       second motor neuron has cell body within ganglion & postganglionic fiber

 

-       Sympathetic Division:

o      short preganglionic fibers arise from thoracolumbar (thoracic & lumbar) region of spinal cord

o      long postganglionic fibers supply the visceral organs, as well as smooth muscle of structures of the skin (sweat glands, arrector pili muscles) & smooth muscle of all arteries and veins

o      postganglionic fibers use neurotransmitter norepinephrine

o      "fight or flight" system... activated during emergency or threatening/stressful situations; rapid heart & breathing rate, greatly decreased gastrointestinal & urinary tract activity, pupils dilated.  Visceral blood vessels are constricted & blood is shunted to active skeletal muscles

 

-       Parasympathetic Division:

o       long preganglionic fibers arise from cranial nerves II, VII, IX & X & sacral region of spinal cord (craniosacral outflow)

o      short postganglionic fibers

o      neurons use neurotransmitter acetylcholine

o      "resting & digesting" system... low energy use (low blood pressure, heart rate & respiratory rate), active digestion of food & elimination of waste; pupils of eyes are constricted & lenses accommodated for close vision

 

Effects of aging:

-       by age 60, thousands of neurons are lost daily, particularly in cerebral cortex

-       neurotransmitter production decreases (slower synaptic transmission)

-       increased incidence of Alzheimer disease

 

Chapter 9: The Sensory System

 

General Receptors:

Skin: contains sensory receptors for touch, pressure, pain & temperature

-       touch receptors: Meissner's corpuscles, Merkel disks & Krause end bulbs

o      Meissner's corpuscles concentrated in fingertips, palms, lips, tongue, nipples, penis & clitoris

-       pressure receptors: Pacinian corpuscles (deep in dermis) & Ruffini endings (encapsulated networks of nerve fibers)

-       temperature & pain receptors: free nerve endings in epidermis

 

Visceral Organs: receptors that aid in homeostasis

-       stretch receptors in lungs respond to lung expansion; receptors in aorta & carotid arteries respond to pH & oxygen levels in blood; osmoreceptors in hypothalamus respond to solute concentration in blood

-       pain receptors in internal organs contact neurons in spinal cord also contacted by pain receptors in skin

-       referred pain: pain in internal organ felt in skin (e.g.: pain in heart is felt in skin of left shoulder & arm)

 

Muscles & Joints:

-       proprioceptors are located within joints & associated tendons & ligaments that respond to stretch, pressure & pain

-       stretch receptors in muscle spindles respond to muscle stretch

o      knee-jerk reflex: when patellar tendon at knee is tapped in crossed leg, muscles & tendons in thigh are stretched & respond by contracting

 

Chemoreceptors: taste in food chemicals & chemical odors in air are sensed by chemoreceptors in the mouth & nose

-       taste buds within papillae on surface of tongue respond to 4 types of taste (sweet, salty, sour & bitter)

-       chemicals in foods bind to microvilli in epithelial taste bud cells & generate nerve impulses that are sent to the gustatory cortex of the brain

 

-       olfactory cells for smell are located at the roof of the nasal cavity

-       olfactory receptor cells are neurons that have olfactory cilia covered by a coat of mucus that dissolves airborne chemicals (odors)

-       there are perhaps more than 1000 types of receptors; the specific odor detected depends on the combination of olfactory cells stimulated

-       the olfactory cells stimulate neurons in the olfactory bulbs, which send the stimulus to the olfactory cortex of the brain

-       taste is possibly about 80% smell... when olfactory receptors are blocked (nasal congestion), taste of food is partially to mostly blocked

 

Photoreceptors: light-sensitive receptors located in the eyes within the orbits of the skull

-       eyebrows & eyelashes: divert sweat & debris from around eyes

-       eyelids: thin skin covered folds of epithelium supported by connective tissue; contraction of the orbicularis oculi muscle closes eyelids & contraction of the levator palpebrae superioris opens eyelids

-       conjunctiva: transparent mucus membrane that lines the eyelids & reflects back over the anterior surface of the eyeballs (except cornea)

-       lacrimal gland: lies within the orbit above the eye; releases a moisturizing lacrimal secretion (tears) containing mucus, antibodies & the antimicrobial enzymes

-       extrinsic eye muscles:

o      lateral rectus: moves eye laterally (control by CN VI)

o      medial rectus: moves eye medially (control by CN III)

o      superior rectus: elevates eye (control by CN III)

o      inferior rectus: depresses eye (control by CN III)

o      inferior oblique: elevates eye & turns it laterally (control by CN III)

o      superior oblique: depresses eye & turns it laterally (control by CN IV)

 

-       structure of the eye

o      sclera: white of eye

       cornea: anterior 1/6 of sclera; transparent CT

o      choroid: highly vascular dark brown membrane; blood vessels supply nutrients to all tunics

       melanin from melanocytes absorb light & prevent scattering

       ciliary body: contains smooth muscle bundles (ciliary muscles) that control lens shape

       lens: binconvex, transparent structure attached to ciliary body

      divides eye into anterior cavity in front of lens & posterior cavity behind lens

      anterior cavity is filled with watery aqueous humor; posterior cavity is filled with gel-like vitreous humor

      glaucoma: due to faulty drainage & thus buildup of aqueous humor in anterior chamber; pressure buildup can damage photoreceptors & lead to partial or total blindness

       iris: lies between cornea & lens; has round central opening called pupil

       pupil opens & closes to control light entry into eye; controlled by smooth muscle in iris

o      retina: consists of 2 layers:

       outer pigmented layer: contains phagocytic pigmented epithelial cells that absorb light & prevent scattering

        inner neural layer: 3 main types of neurons

      photoreceptors: rods & cones

*      rods: respond to dim light; blurry shades of gray

*      cones: respond to bright light; sharp, color vision

      bipolar cells: link between photoreceptors & ganglion cells

      ganglion cells: receive input from bipolar cells & their axons leave eye as optic nerve

       blind spot (optic disc): location on retina where the optic nerve exits eye

        fovea centralis: only cones present; region of greatest visual acuity

 

-       rods: contain rhodopsin, which consists of the pigment retinal (a vitamin A derivative) linked to  a form of opsin (protein)

o      rods are sensitive to faint light (night) & motion, but do not detect color or fine detail

o      hence, at night objects are seen as blurry & in shades of gray

o      when light strikes rhodopsin, it breaks down & generates a nerve impulse

o      in dim light, the pupils dilate to allow more light to reach the retina; at the same time, rhodopsin forms to improve vision -> 2 delays to adjustment to dim light

-       cones: contain one of 3 opsins with retinal, allowing absorption of 3 different colors of light (red, green & blue)

o      cones are sensitive to bright light & detect fine detail & color

o      color observed depends on combination of cones (RGB) stimulated

o      color blindness: usually, one type of cone is deficient (red or green cone deficiency is most common -> red-green color-blindness)

 

-       stereoscopic vision: each eye forms image from different angle & sends independent stimulus to brain

o      optic nerve fibers cross at optic chiasma, & one hemisphere of brain receives information from both eyes about the same part of an object

o      the 2 hemispheres share information to arrive at complete 3D image

-       lens: the cornea, vitreous humor & lens all participate in refraction of light to focus it on the retina

o      accommodation: bulging of lens by contraction of ciliary muscle to view close objects (no accommodation is required to view distant objects)

o      if accommodation is not enough to focus image, prescription lenses may be required

o      cataract: lens becomes opaque (perhaps due to oxidation of lens proteins) & unable to transmit light to retina (lens can be surgically replaced with plastic lens)

 

Mechanoreceptors: receptors in the inner ear provide senses of equilibrium (balance) & hearing

-       external ear: consists of pinna (auricle or visible portion of ear) & external auditory canal

o      ceruminous glands: modified sweat glands in upper wall of canal that secrete earwax, which protects against particle entry into middle & inner ear

-       middle ear: begins at tympanic membrane (eardrum) & ends at 2 small openings (oval & round window) to inner ear

o      contains 3 ossicles (small bones) suspended by ligaments

       malleus (hammer) - attaches to eardrum

       incus (anvil)

       stapes (stirrup) - attaches to oval window of vestibule (inner ear)

o      the anterior wall of the middle ear contains an opening to the auditory (eustachian) tube (leads to nasopharynx) that allows pressure equalization

o      otitis media: middle ear infection causing inflammation & blockage

       myringotomy: incision in eardrum, followed by insertion of tube to equalize pressure (can be surgically removed later)

-       inner ear:

o      vestibule: central region composed of 2 sacs - the saccule & utricle

       contains static equilibrium receptors called maculae

o      semicircular canals: 3 rounded tubes projecting from utricle through swellings called ampullae

       ampullae contain dynamic equilibrium receptors called cristae ampullaris

o      cochlea: snail-shaped chamber extending from the saccule

       contains cochlear duct housing the organ of Corti, which contains receptors for hearing

 

-       Hearing:

o      sound waves enter the auditory canal & cause the tympanic membrane to vibrate

o      the ossicles receive the vibration, amplify & transmit it to the oval window, causing pressure waves in the cochlear fluid

o      the pressure waves move from the vestibular to cochlear to tympanic canal within the cochlea, causing bulging of the round window & reverberation of fluid

o      the fluid movement moves the cilia of the hair cells within the organ of Corti, initiating nerve impulses which are transmitted along the cochlear branch of the vestibulocochlear nerve to the auditory cortex of the temporal lobe of the brain, which interprets the sound

 

-       Equilibrium:

o      dynamic equilibrium: required when a person is in angular or rotational motion

       fluid within the semicircular canals flows over the ampullae, causing displacement of the cilia of hair cells

       the hair cells generate impulses that are transmitted along the vestibular branch of the vestibulocochlear nerve to the brain

       continuous fluid movement in semicircular canals can cause motion sickness

o      static equilibrium: required when the body moves horizontally or vertically

       otoliths (calcium carbonate granules) in the vestibule are displaced from the otolithic membrane, & the membrane sags

       the sagging membrane bends the cilia of the hair cells, which generate impulses that are transmitted along the vestibular branch of the vestibulocochlear nerve to the brain

 

Effects of Aging:

-       the need for eyeglasses & hearing aids increases with age

-       incidence of cataracts, glaucoma & age-related macular degeneration increases with age

-       overgrowth of the stapes (otosclerosis) & atrophy of the organ of Corti (presbycusis) can lead to the development of hearing loss later in life

 

 

 

Chapter 10: The Endocrine System

 

Endocrine System: a system of small glands scattered throughout the body that influences the metabolic activities of cells through hormones

-       Hormones: chemical messen