CH: 9 Nervous System: Basic Structure and Function

What is the NS composed of

MOSTLY nervous tissue

blood vessels

CT

two cell types of nervous tissue

neurons

neuroglial cells

neurons

specialized to react to physical + chemical changes in surroundings

can engage in AP

dendrites

cellular processes that receive input

branches to provide receptive surfaces to which processes from other neurons can communicate

Neurons can have MANY dendrites but only ONE axon

dendritic spines

tiny spines on surface of dendrites

axons

long cellular processes that carry impulses away from neuron

vary in sizes

axon hillock

initial portion of axon

closest to cell body

axon terminals

end of axon

has synaptic end bulbs

made up of multiple telodendria

collaterals

branches of axons (extra)

axonal transport

process an axon uses to convey biochemicals that are produced in cell body

schwann cells

produce myelin

has neurilemma

only PNS

neurilemma

portion of schwann cell

outside myelin sheath

myelin

lipid-rich substance

produces myelin sheath

myelin sheath

coats axon

speeds up transactions

insulates

Myelinated axons have

unmyelinated axons dont have

what is white matter made of?

myelinated axons

what is gray matter made of?

unmyelinated axons

dendrites

cell bodies of neurons

node of ranvier

narrow gap between myelin sheaths

impulses

bioelectrical signals produced by neurons

nerve definition

bundle of axons

synapse

small space between neuron and the cells it communicates with

AKA synaptic cleft OR neuromuscular junction in muscle cells

synaptic knob

specialized ending of an axon

swollen

vesicles filled with neurotransmitters

neurotransmitters

biological messengers produced by neurons`

central nervous system

CNS

contains brain and spinal cord

• skull

• Cerebral spinal fluid

  • meninges (D.A.P)

• vertebrae

signals are integrated —> decisions are made and acted upon by motor functions

Peripheral nervous system

PNS

contains cranial and spinal nerves

• nerves connected to brain: 12 pairs

• spinal nerves have 31 paits

receives info from outside CNS

has motor neurons

• located in the autonomic nervous system

  • sympathetic NS

  • enteric NS

    • digestive system organs

  • parasympathetic NS

• signals are integrated

  • decisions are made and acted upon by means of motor function

• skeletal motor

has sensory neurons

• dorsal root ganglia

  • cranial nerve ganglia

three functions of NS

sensory

integrative

motor

sensory receptors

located at the ends of peripheral neurons

provide sensory function of nervous system

receptors

gather information

• tells NS the intensity of pain

convert info into nerve impulses

• transmitted over the peripheral nerves to the central nervous system

motor functions

use neurons to carry impulses from CNS to effectors

effectors

start the action

muscles and glands (motor neurons)

motor divisions

somatic and autonomic

somatic NS

motor division

involved in conscious activities

skeletal

autonomic NS

motor division

involved in unconscious activities

cardiac and smooth muscles and glands

divisions of autonomic NS

sympathetic division

parasympathetic division

enteric NS

brain

receives + processes sensory information

initiates responses

stores memories + generates thoughts + emotions

spinal cord

conduct signals to and from the brain

controls reflex

sympathetic division

fight or flight

parasympathetic division

rest of digest

SLUDD

• Salivation: saliva

• Lacrimation: tears

• Urination: pee

• Digestion

• Defecation: p00p

3 (4) structural types of neurons

1. multipolar

2. bipolar

3. unipolar

4. (pseudo-unipolar)

neuron’s cell body

SOMA

contains:

• granular cytoplasm

• mitochondria

• lysosomes

• Golgi apparatus

• large nucleus

neurofibrils

fine threads that extend into axon

Nissl bodies

chromatophilic substance

located on cell bodies

membranous sacs that contain rough Er

named after Franz Nissl

what cells divide?

mature neurons usually DO NOT divide

neural stems DO divide

how many axons and dendrites do neurons usually have?

ALWAYS one axon

can vary in amount of dendrites but can have more than one

bipolar neuron

two processes

1. dendrite

2. axon

found in eyes, ears, nose (PNS)

unipolar neuron

one process

1. axon

peripheral process is associated dendrites near a peripheral body part and central process enters brain or spinal cord

located in ganglia

• cluster of neuron cells in the PNS

multipolar neuron

multiple dendrites + ONE axon

located in brain and spinal cord

CNS

three classes of functional differences

sensory

motor

interneurons

sensory neuron

carry nerve impulses from peripheral body parts into the brain or spinal cord

PNS

have specialized sensory receptors at the distal ends of dendrite

usually unipolar but some are bipolar

interneurons

located in brain and spinal cord

multipolar

form links between other neurons

motor neurons

carry nerve impulses from the brain and spinal cord to effectors

control skeletal muscles, glands, smooth muscle, cardiac muscle

found in CNS

pseudounipolar neurons

can be classified as just unipolar

PNS

one short axon that splits into two processes

• central process

  • The branch that extends from the cell body (soma) towards the CNS, carrying sensory signals from the peripheral process into the spinal cord/brain

• peripheral process

  • The branch extending from the cell body out to the body's periphery (skin, muscles, organs) to detect sensory stimuli like touch, pain, and temperature

anaxonic neuron

Axon cannot be distinguished from many dendrites

CNS in the brain and in special sense organs

neuroglial

binds and supports NS

6 types

smaller than neurons

mitotic (will replicate)

tumors result in division

four types of neuroglial cells of CNS

astrocytes

oligodendrocytes

microglial cells

ependymal cells

astrocytes

star shaped

found between neurons and blood vessels

most numerous

helps neurotransmitters + monitors potassium levels

provide support and hold structures together

aid metabolism of glucose for brain energy

respond to injury of brain tissue to form special scar tissue

plays role in the BBB

blood-brain barrier

astrocytes

blood vessels designed to prevent things from entering the brain

restricts movement of substances between blood and CNS

oligodendrocytes

rows along myelinated axons

form myelin in brain and spinal cord

does not form neurilemma like schwann cells

microglia

smallest neuroglia

removes dead neurons + neuroglia

secretes stuff to kill bacteria

function to support neurons

ependymal cells

form inner lining of central canal of spinal cord and ventricles of brain (spaces)

• helps produce CSF + move it through ventricles

neuroglia found in PNS

schwann cells

satellite cells

satellite cells

PNS

support clusters of neuron cell bodies (ganglia)

protection and repair

what happens when neuron is damaged

cell body: neuron suicide

axon: slowly regenerates

presynaptic neuron

neuron that brings impulse to synapse

postsynaptic neuron

neuron that stimulated by presynaptic neuron

synaptic transmission

process by which impulse in presynaptic neuron signals post synaptic neuron

polarization

unequal distribution of positive and negative ions on either side of membrane

when cell membrane is polarized, inside is negative and outside is positive

intracellular positive ion

potassium (K+)
positive ion located inside the cell

extracellular cation

Sodium (Na+)

positive ion located outside the cell

what is used to transport Na+ and K+ through sodium-potassium pumps

ATP

volts

electrical differences between two points

potential difference because it represents stored electrical energy that can be used to do work

millivolts

the units used to measure potential difference across a cell membrane

-70

neurons are __________ because they respond to changes in surroundings

excitable

hyperpolarized

membrane potential becomes more negative than resting potential

depolarization

membrane is less negative than resting potential

threshold potential

sufficient depolarization that triggers action potential

trigger zone

the initial segment of axon

contains many voltage-gated sodium channels

repolarization

membrane is polar again or returned to original resting state

which parts of the neuron are capable of action potential

axons

not soma or dendrites

all-or-nothing response

if neuron responds at all to a nerve impulse, it responds completely

refractory period

stimulus will NOT trigger another impulse bc the axon needs to repolarize

limits how many action potentials may be generated

absolute refractory period

Axon’s membrane cannot be stimulated

First part of the refractory period

relative refractory period

stronger stimulus can trigger impulse

saltatory conduction

nerve impulse that occurs only at nodes of ranvier

nerve fiber classification

classified according to diameter, degree of myelination, speed of conduction

• group A

• group B

• group C

group A fibers

fastest

large diameter

myelinated sheath

somatic sensory and motor fibers

group B fibers

intermediate diameter

lightly myelinated ANS fibers

heart and glands

group C fibers

slowest

smallest diameter

unmyelinated ANS fiber

no sheath

where do released neurotransmitters diffuse to

across synaptic cleft and react with molecules that form receptors in or on postsynaptic neuron membrane

synaptic potentials

local potentials created by changes in chemically gated ion channels

synaptic potentials

can depolarize or hyperpolarize the receiving cell membrane

excitatory postsynaptic potential

type of change where cell membrane is depolarized

causes Na+ channels to open (leaves)
EX: glutamate

inhibitory postsynaptic potential

cell membrane is hyperpolarized

causes Cl- channels to- open (leaves)

acetylcholine

stimulates skeletal muscle contractions

thinking + comprehension

monoamines

epinephrine

norepinephrine

dopamine

serotonin

unmodified amino acids

glycine

glutamic acid

aspartic acid

GABA

peptides

synthesized in R.E.R

ex: substance P, enkephalins

reuptake

neurotransmitters are transported back into synaptic knobs of presynaptic neurons

glutamte

memory

GABA

eating

sleeping

aggression

dopamine

movement

attention

pleasure + reward