A&P I lecture exam 4

Nervous system functions

1- conduction of signals from sensory receptors to processing center

2- processing of brain and spinal cord- interprets these sensory signals and forms a response

3- conducts a signal to an effector

Central nervous system

brain + spinal cord

peripheral nervous system

cranial and spinal nerves

somatic nervous system

voluntary = skeletal muscle

autonomic nervous system

involuntary = smooth and cardiac muscle, glands

nervous system cell type 1 - neurons

conduct electrical signals or action potentials/impulses

nervous system cell type 2- neuroglia

makes up 90% of nervous system cells

support cells

framework for nervous tissue

protection

control composition of extracellular fluid = cerebrospinal fluid in CNS

ependymal cells

assist with producing, monitoring and circulation of CSF

microglial cell

engulf cellular debris, waste and pathogens

astrocyte

many functions:

-maintenance of blood/brain barrier

-structural support

oligodendrocyte

-myelinate CNS axons

-structural support

General Features of a Neuron- Properties

1. Generally amitotic- cannot be replaced

2. Extreme longevity

3. High metabolic rate

Parts of a neuron- cell body(soma)

nucleus, golgi, mito, RER

lack centrioles

abundant cytoskeletal components- neurofibrils

Perikaryon- cytoplasm surrounding nucleus

parts of neuron- axon hillock

initial segment

parts of neuron- axon

carries signals (action potentials) away from cell body

two types of axons

naked- unmyelinated

myelinated- covered with myelin sheath

parts of neuron- dendrites

receives signal

parts of neuron- telodendria

contains axon terminals= synaptic knobs

Formation of the Myelin Sheath

formed by neuroglia

the two cells that form the myelin sheath

1. oligodendrocytes (CNS)

2. Schwann Cells (PNS)- these cells form myelin sheath by wrapping their cytoplasm and membranes around the axon

Nodes of Ranvier(naked axon)

action potentials are conducted from node to node = saltatory conduction(very fast and efficient way to carry an action potential down an axon

functions of myelin sheath

1. Protection

2. Increases speed of action potential conduction b/c myelin is an insulating material

bipolar classification of neurons

Rare: generally associated with special senses

unipolar classification of neuron

structure common to most sensory neurons

multipolar classification of neuron

structure of most motor neurons and interneurons

sensory neurons (afferent)

carry signals from periphery to CNS

motor neurons (efferent)

carry signals from CNS to muscles and glands

interneurons (association)

most abundant

carry signals b/t sensory and motor neurons

major brain regions

cerebrum- convoluted

major brain regions

diencephalon- cannot be seen externally

a. thalamus- superior portion

b. hypothalmus- inferior portion

major brain regions

brainstem

1. midbrain or mesencephalon

2. pons varolii

3. medulla oblongata

major brain regions

cerebellum

major brain regions

spinal cord

Development of the central nervous system- neural tube

nervous system forms from a hollow tube called a neural tube

protection of the brain and spinal cord- bones

cranium-

frontal

parietal

occipital

ethmoid

sphenoid

temporal

spinal cord is located within the

vertebral canal (c1 through L1 or L2)

protection of the brain and spinal cord- meninges

connective tissue layers

3 layers: duramater

arachnoid mater

pia mater

(all cover both the brain and spinal cord)

3 important variations of cranial meninges

1. no epidural space

outer fibrous layer fused to periosteum of the cranial bones

3 important variations of cranial meninges

2. space within dura mater at midline called:

superior sagittal sinus- delivers venous blood to internal jugular vein

arachnoid villi- connects subarachnoid space to superior sagittal sinus (CSF is reabsorbed into venous blood at arachnoid villi)

Three folds of dura mater-

subdivide the cranial cavity

the three folds of dura mater- falx cerebri

b/t cerebral hemispheres in longitudinal fissure

the three folds of dura mater- falx cerebelli

divides cerebellar hemispheres

the three folds of dura mater- tentorium cerebelli

separates the cerebral and cerebellar hemispheres

functions of the folds

limits excessive movements of the brain within the cranial cavity

cerebrospinal fluid

fluid that surrounds and bathes the entire brain and spinal cord

function of cerebrospinal fluid

acts like a cushion- protects brain from sudden jolts and shocks

supports brain

transports chemical messengers, nutrients and waste products

production of cerebrospinal fluid

produced in choroid plexus: originates in 3rd ventricle, lateral ventricle and 4th ventricle

circulation of CSF

1. lateral ventricle CSF is produced

2. 3rd ventricle CSF is produced

3. 4th ventricle CSF is produced

4. CSF flows into subarachnoid space through the lateral and medial apertures, and into the central canal of the spinal cord

5. excess CSF drains into the arachnoid vili and then into the dural venous sinuses

Anatomy & Physiology of the brain

cerebrum contains 3 parts:

a. Surface gray matter (cerebral cortex)

outermost layer

neuron cell bodies and unmyelinated axons

b. white matter

myelinated axons

c. deep gray matter (cerebral nuclei)

cerebral nuclei

sulcus or sulci

shallow groove

fissure

deep groove

gyrus or gyri

elevated ridge

sensory function

receive and interpret incoming signals

motor function

control movement

association function

involved in intellectual and emotional processes also will integrate info

primary motor area

precentral gyrus, controls voluntary movement of specific muscles

pre-motor areas

stored pathways for learned activities

pre-frontal cortex

abstract intellectual processes consequences of behavior

brora's area

only on left side, motor speech- moves muscles for speech

olfactory area

smell

primary sensory area

postcentral gyrus, receives incoming sensations - localizes them to specific body regions

somatosensory area

association area: interpret, analyze and evaluate sensory info

wernicke's area

language comprehension and interpretation

general interpretative areas (gnostic area)

usually all over left side, stores memories associated w/ sensations, damage would affect your ability to interpret what is seen or heard

white matter - tracts

bundles of myelinated axons located within the CNS

Three types of tracts

association, commissural and projection

association tracts

connects and transports signals b/t gyri of same hemisphere

arcuate fibers and longitudinal fasciculi

commissural tracts

connects and transmits signals from a gyrus on one hemisphere to the corresponding gyrus on the other hemisphere

corpus callous and anterior commisure

projection tract

link the cerebral cortex to diencephalon, brain stem, cerebellum and spinal cord

projection fibers of internal capsule

function of the basal nuclei

control of subconscious muscle movements

- stimulate muscles to produce pattern and rhythm of arm and leg movements associated w/ walking

- help to control and adjust muscle tone during voluntary movements

thalamus structure

1. 2 masses of gray matter covered by white matter

2. contains numerous nuclei

3. located on each side of the third ventricle

thalamus function

relays sensory info to basla nuclei and cerebral cortex, acts as a filter = sends only small portions of sensory info to basal nuclei or cerebral cortex. examples: touch, pressure, pain, temp, position, visual and auditory

hypothalamus structure

1. contains many nuclei

2. forms ventral floor of third ventricle

hypothalamus function

maintenance of homeostasis

controls autonomic nervous system and endocrine system

examples- sleep/wake patterns, hunger, thirst, body temp, emotions, sexual responses

midbrain

extends from pons to lower diencephalon

pons varolli

superior to medulla and anterior to cerebellum

pons varonil function

contains pathways that link cerebellum w/ cerebrum, brain stem and spinal cord

also contains nuclei for cranial nerves V, VI, VII, and VIII

medulla oblongata

inferior brainstem, continuous with spinal cord

medulla oblongata function

conducts sensory and motor info

contains vital and non-vital reflex center

vital

cardiac center, respiratory center and vasomotor center

non-vital

swallowing, sneezing vomitting

cerebellum

second largest part of brain

2 hemispheres connected by vermis

cerebellum contains

cortex(surface gray matter), white matter, and cerebellar nuclei(masses of gray matter)

function of cortex and cerebellar nuclei

1. Maintenance of balance and equilibrium

2. motor coordination for muscle movements = allows for smooth controlled movements

hemisphericity

the right hemisphere controls movements on the left side of the body and the left hemisphere controls movements on the right side of the body

limbic system location & function

located in parts of cerebrum located on border b/t cerebrum and diencephalon

functions involved in memory, creates emotional states (pleasure, pain, rage, behaviors related to survival, motivation)

reticular activating system location & function

located in many parts of brain working together

functions as sleep/wake cycle, when RAS is stimulated = cerebral cortex becomes active

PNS cranial nerves

olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal

PNS cranial nerves saying

oh once one takes the anatomy final, very good vacations are heavenly(name order)----------some say money matters but my brother says bad bitches matter most(sensory/motor, b=both=mixed)

olfactory nerve

I

sensory function

transmits impulses related to smell from nose to olfactory bulb

optic nerve

II

sensory function

transmits impulses related to vision from retina

oculomotor nerve

III

motor function

conveys impulses that control eye movement regulation of pupil size and accommodation of lens for near vision

trochlear nerve

IV

motor function

conveys impulses that control eye movement

trigeminal nerve

V

mixed function

sensory: conveys impulses relating to sensations of head and face

motor: conveys impulses that control chewing

abducens nerve

VI

motor function

conveys impulses that control eye movement

facial nerve

VII

mixed function

sensory: conveys sensations related to taste from tongue to brain

motor: conveys impulses that control facial expression

vestibulocochlear nerve

VIII

sensory function

vestibular: conveys impulses associated with equilibrium from inner ear to brain = balance

cochlear: conveys impulses associated with hearing from organ of corti in cochlea to brain