PCOM: Anatomy 3 - week 2, reader Pg 17 - 29

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characteristics of Group A fibers

largest in diameter, thick myelin sheaths, conduct nerve impulses rapidly

function of Type A fibers

mostly somatic sensory and motor innervating the skin, skeletal muscles and joints

characteristics of Type B fibers

slightly myelinated, intermediate in diameter, conduct much more slowly than Type A, but faster than Type C

characteristics of Type C fibers

unmyelinated and smallest in diameter; conduct impulses slowly

function of Type B and Type C fibers

predominately autonomic , visceral sensory and smaller somatic from skin (pain and light touch)

definition of synapse

the junction between neurons or a neuron and effector organ that allows information in the form of an action potential to be passed along

axodendritic synapse

synapse between the axon of one neuron and the dendrite of another - most common

axosomatic synapse

synapse between the axon of one neuron and the cell body of another

axoaxoninc synapse

synapse between the axon of one neuron and the axon of another - uncommon

term for neurons that transmit action potentials toward the synapse

presynaptic neuron

term for neurons that transmit action potentials away from the synapse

postsynaptic neuron

the 2 types of synapses

electrical and chemical

structure of electrical synapses

consist of gap junctions containing a protein channel (like a bridge) that connect the cytoplasm of neighboring neurons, allowing substances (ions and small molecules) to flow from one neuron to the next

term for the protein channels in the electrical synapses

connexons

mechanism of chemical synapses

no gap junction - communication is via neurotransmitters release from the presynaptic neuron

term for the space between presynaptic and postsynaptic neurons in chemical synapses

synaptic cleft

presynaptic structures of chemical synapses

synaptic vesicles in the knob-like contain 1000's of neurotransmitters

postsynaptic structures of chemical synapses

a protein receptor area on the postsynaptic cell to receive the neurotransmitters

Area separating the presynaptic and postsynaptic neurons

synaptic cleft - filled with interstitial fluid

ion that causes the synaptic vesicles to fuse with the axon membrane and release neurotransmitters

Ca2+

stages of information transfer across the synaptic cleft

1 - Action potential arrives at the axon terminal of the presynaptic neuron
2 - depolarization fo the axon terminal opens Na+ and Ca2+ voltage gates
3 - Ca2+ rushes into the axon terminal
4 - Ca2+ causes the synaptic vesicles to merge withe the axon terminal membrane and release neurotransmitters
5 - neurotransmitters diffuse across the synaptic cleft and bind with receptors on the postsynaptic membrane
6 - binding neurotransmitters open ion channels causing excitatory or inhibitory hyperpolarization graded potentials depending on the neurotransmitter
7 - neurotransmitters are removed from the postsynaptic receptors, usually by enzymes

type of gates neurotransmitter receptors are

chemically gated or ligands

factors influencing the graded potential created on the postsynaptic membrane by neurotransmitters

vary by how much neurotransmitter is released into the synaptic cleft and by how long the neurotransmitters remain on the receptors

term for the accumulation of stimuli creating a graded potential

summate

two types of summation

temporal and spatial

temporal summation

strength of the graded potential increases (greater depolarization) due to repeated neurotransmitter stimulus within a relatively short timeframe

spatial summation

strength of the graded potential increases due to 2 or more simultaneous neurotransmitter stimuli at different locations on the postsynaptic membrane

term for excitatory potentials created on the postsynaptic membrane by certain neurotransmitters

excitatory postsynaptic potential (EPSP)

function of the EPSP

to create and action potential at the axon hillock of the postsynaptic neuron by creating ionic currents along the dendrite which, if strong enough, depolarize the axon hillock and open Na+ voltage gated channels

term for inhibitory potentials created on the postsynaptic membrane by certain neurotransmitters

inhibitory postsynaptic potential (IPSP)

function of the IPSP

hyperpolarization of the postsynaptic membrane by the opening of K+ influx or Cl- efflux ligands by specific neurotransmitters, but not affecting Na+ channels

Types of neurotransmitters

Acetylcholine, biogenic amines, amino acids, peptides, purines, gases

term for the synapse between motor neurons and the skeletal muscle

neuromuscular junction

neurotransmitter released at the neuromuscular junction

Ach - Acetylcholine

abbreviation for acetylcholine receptors

AchR

name of the enzyme that breaks down Ach

acetylcholinesterase - ACHE

two types of biogenic amines

catecholamines and indolamines

the three catecholamines

epinephrine, norepinephrine, dopamine

two types of indolamines

seratonin and histamine

amino acid used in the synthesis of dopamine and norepinephrine

tyrosine

amino acid used in the synthesis of seratonin

tryptophan

two key types of peptides

substance P and endorphins

function of substance P

to mediate pain signals

function of endorphins

natural opiates which reduce pain

function of purines

ATP - can trigger fast or slow excitatory response dependent on the ATP receptor

component of ATP that acts as a potent inhibitor

adenosine - blocked by caffeine, creating a stimulatory effect

main gas neurotransmitter

nitric oxide

function of nitric oxide as a neurotransmitter

short-lived, not stored in vesicles which participate in a variety of brain processes

classifications of neurotransmitters

excitatory, inhibitory or both

what determines the function of neurotransmitters

the receptor on the postsynaptic membrane to which they bind

two ways neurotransmitters act on the postsynaptic neuron

directly and indirectly

how neurotransmitters work directly

open ion channels

how neurotransmitters work indirectly

via a 2nd messenger chemical which influences ion channels, activate enzymes or activates genes

two key types of 2nd messenger molecules

cyclic AMP and Ca2+

embryonic layer ultimately giving rise to the CNS

ectoderm

differentiation of the ectoderm in the embryo at 2 weeks

forms the neural plate which invaginates, forming the neural groove

progression of the embryonic neural groove from week 2 to week 4

fuses at the superior edges forming the neural tube which then descends to a deeper position

structure that becomes the CNS

the neural tube

portion of the neural tube that becomes the three primary brain vesicles

the anterior portion of the neural tube

how the brain vesicles form

the anterior neural tube expands and constricts in three places, forming the three vesicles

the three primary brain vesicles

prosencephalon (forebrain), mesencephalon (hindbrain), and rhombencephalon (midbrain)

what the posterior neural tube forms

the spinal cord

what occurs in the formation of the CNS in week 5 of development

the 3 primary vesicles give rise to the 5 secondary vesicles

the 5 secondary vesicles

telencephalon, diencephalon, metencephalon, myelencephalon, mesencephalon

secondary vesicles arising from the forebrain

telencephalon and diencephalon

secondary vesicles arising from the hindbrain

metencephalon and myelencephalon

structures in the adult brain arising from the telencephalon

cerebrum: cerebral hemispheres (cortex, white matter, basal nuclei)

structures in the adult brain arising from the diencephalon

thalamus, hypothalamus, epithalamus, retina

structures in the adult brain arising from the metencephalon

brainstem: pons and cerebellum

structures arising from the myelencephalon

brainstem: medulla oblongata

structures arising from the mesencephalon

brainstem: midbrain

structures of the brainstem, superior to inferior

midbrain, pons, medulla oblongata

what happens as the cerebral hemisphere continues to grow and form

due to restricted space in the skull cavity, the cerebral hemispheres mushroom out and grow over the diencephalon and midbrain and fold and creases appear, forming greater surface area in the brain

what the lumen of the neural tube forms

the 4 ventricles

subdivisions of the adult brain

cerebral hemispheres, diencephalon, brainstem, cerebellum

grey matter of the CNS

neuron cell bodies and unmyelinated axons

white matter of the CNS

myelinated axon tracts

characteristics of the structure of the 4 ventricle

continuous with each other and the central canal of the spinal cord

what filles the ventricles

cerebrospinal fluid

what lines the ventricles

ependymal cells

ventricles of the cerebral hemispheres

paired lateral ventricles - one in each hemisphere

ventricle of the diencephalon and its characteristics

the 3rd ventricle which is continuous with the lateral ventricles

the channel that connects the lateral and 3rd ventricles

intraventricular foramen or Foramen of Monroe

ventricle of the brainstem and it characteristics

the 4th ventricle which is continuous with the 3rd ventricle and has 3 openings in its walls

the openings of the 4th ventricle's walls

paired lateral apertures on its sides and the median aperture on its roof

the canal that connects the 3rd and 4th ventricles

the cerebral aqueduct

with what the 4th ventricle is continuous

the central canal of the spinal cord

significance of the apertures of the 4th ventricle

open to the CSF filled subarachnoid space surrounding the brain and spinal cord

name for the elevated ridges of the cerebral hemisphere

gyri

name of the grooves between the ridges of the cerebral hemisphere

sulci

the deeper grooves of the brain separating large areas of the brain

fissures

fissure separating the cerebral hemispheres

longitudinal fissure

fissure separating the cerebral hemispheres from the cerebellum

transverse fissure

5 lobes of the cerebral hemispheres

frontal, parietal, occipital, temporal, insula

sulcus separating the frontal lobe from the parietal lobe and its orientation

the central sulcus is located on the coronal plane

name of the gyri on either side of the central sulcus

the pre-central and post-central gyrus

name of the sulcus separating the temporal and parietal lobes

lateral sulcus

lobe of the cerebral hemisphere that lies deep to the lateral sulcus and the temporal, parietal and frontal lones

insula

regions of the cerebral hemisphere

cortex, white matter, basal nuclei

structure of the cortex

gray matter - groups of nerve cell bodies, dendrites, neuroglia and blood vessels

structure of the white matter

myelinated axons

structure of the basal nuclei

gray matter - groups of nerve cell bodies within the cerebrum

functions of the cerebral cortex

conscious mind, perception of sensations, communications and muscles activity, memory, awareness of surroundings

three functional areas of the cerebral cortex

motor, sensory, association

types of neurons in the cerebral cortex

interneurons

characteristic of sensory and motor control of the cerebral hemispheres

contralateral - controls the opposite side of the body

characteristic of the integration of the different areas of the cerebral cortex

all areas work together in conscious behavior - no area acts alone and the entire cortex is involved

characteristic of the functions of the hemispheres

lateralization - each hemisphere has unique functions and abilities

location of the motor area of the cerebral cortex

posterior part of the frontal lobes

location of the primary motor cortex

the precentral gyrus of the frontal lobes of each hemisphere

neurons of the precentral gyrus responsible for voluntary movement of skeletal muscles

pyramidal cells

structures and locations of the axons of the pyramidal cells

form pyramidal or corticospinal tracts which are located throughout the spinal cord

structure that forms in the primary motor cortex representing the different areas of the entire body

motor homunculus

characteristic of motor innervation of the primary motor gyrus

contralateral - controls the opposite side of the body

location of the premotor cortex

anterior to the precentral gyrus

functions of the premotor cortex

controls learned motor skills or a repeated or patterned nature, influences the primary motor cortex and motor activity and supplies about 15% of the corticospinal tracts

location of Broca's Area

anterior to the inferior region of the premotor cortex and usually only in one hemisphere - usually the left

function of Broca's Area

muscular/motor function of speech; becomes active when preparing to speak or in the planning many voluntary motor activities

location of the frontal eye field

partially anterior to the Premotor cortex and superior to Broca' Area

function of the frontal eye field

voluntary movement of the eyes

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