AP 1, Unit 3, Ch 11 - Organization of Nervous Tissue

Anatomy and Physiology 1 - Organization of Nervous Tissue

what are the two types of cells in the nervous system?

neurons and glia cells

neurons

the electrically excitable cells of the NS, consist of axon, body and dendrites

cranial nerves

originate from the brain, 12 pairs

spinal nerves

originate from the spinal cord, 31 pairs

plexus

a bundle of nerves outside the brain and spinal cord

What are the functions of the nervous system?

1. maintaining homeostasis

2. receiving sensory input

3. integrating information

4. controlling muscles and glands

5. establishing and maintaining mental activity

what are the two major divisions of the NS?

1. central nervous system

2. peripheral nervous system

what does the CNS do?

receives information from the body and sends information out to the body

what does the PNS do?

responsible for detecting stimuli in and around the body, sending that info to the CNS. CNS sends info to PNS to deliver out to the body.

What are the two primary divisions of the PNS?

sensory (afferent division) and motor (efferent division)

describe sensory division process

sensory receptors receive stimuli, sends along nerves to brain or spinal cord, at which point the body creates a response

describe motor division process

transmits signals from CNS to effector organs like muscles.

what are the two divisions of the motor division

somatic nervous system and autonomic nervous system

somatic division of motor div

voluntary movement

autonomic division of motor div

involuntary movement

what are the three subdivisions of the autonomic motor division?

1. sympathetic - fight or flight

2. sympathetic - rest and digest

3. enteric - neuronal networks within the digestive tracts

neuron cell body

performs typical cell functions (ie protein synthesis and packaging protein into vesicles)

dendrites

extensions of the neuron cell body, receive info from other cells.

dendritic spines

when axons of other neurons make connections with with dendrites

axon

where action potentials are generated

synapse

a point of space between an axon and its effector

presynaptic terminal

the region of the axon which ends at the synapse

synaptic vesicles

store the signal molecules produced by the neuron

neurotransmitters

control the effectors and are called neurotransmitters

anterograde

movement away from the cell body

retrograde

movement toward the cell body

what are the three types of neurons

1. sensory (afferent neurons)

2. motor (efferent neurons)

3. interneurons (conduct APs within the CNS from one neuron to another)

What are the different categories of axons based on number of dendrites?

1. multipolar (many dendrites, single axon)

2. bipolar (one dendrite, one axon)

3. psuedo-unipolar (two processes that extend from the cell body fuse into ONE process)

4. anaxonic (no axons, only dendrites)

What are the four types of glial cells?

1. astrocyte

2. ependymal cells

3. microglia

4. oligodendrocytes

astrocytes function

help form framework for blood vessels and neurons. regulate composition of extracellular brain fluid. In blood brain barrier.

blood-brain barrier

permeability barrier controlling pasage of compound from blood to the CSF and brain

ependymal cell functions

line ventricles of the brain and central canal of spinal cord

choroid plexuses

secrete CSF, formed by ependymal cells

microglia cell function

CNS specific immune cells . Phagocytic in response to inflammation.

oligodendrocytes

form an insulating layer around axons, forms the myelin sheath

myelin sheath

helps to conduct impulses, formed by schwann cells. high lipid concentration.

what are the two types of glial cells in the PNS?

1. schwann cells

2. satellite cells

satellite cells

surround neural cells bodies , provide support, nutrition, and protect cell bodies from heavy metal poisons by absorbing them

nodes of Ranvier

gaps in myelin sheath, allow for ions to diffuse in and out of the membrane to move the electrical signal quickly down the axon. part of saltatory conduction.

unmyelinated axons

not completely unmyelinated. axons rest in invaginations along the side of schwann cells.

gray matter

darker in appearance d/t little myelination. consists of groups of neuron cell bodies and dendrites. Cortex is the gray matter on the surface of the brain.

white matter

bundles of parallel myelinated axons, white in appearance d/t myelination and lipids.

potential difference

electrical charge difference across th plasma membrane

hypocalcemia

low levels of Ca2+. Since Ca keeps voltage gated channels closed, low Ca levels can cause spontaneous openings, symptoms can include nervousness and uncontrolled muscle contraction

hyperpolarization

when inside the cell becomes even more negative compared to outside. less likely to generate an AP, inhibitory to the cell

hypokalemia

lower concetration of K in blood levels. symptoms include muscular weakness, abnormal heart function, sluggish reflexes. can be caused by starvation, alkalosis and kidney disease.

graded potentials

a larger potential = a larger stimulus. when a second stimulus is applied to a cell before the first dissapears, the second added to the first results in an even larger stimulization.

summation

a combination of graded potentials

refractory period

period following stimulation of a cell when the cell becomes less sensitive to subsequent stimuli, two parts.

absolute refractory period

first part of the refractory period. period following stimulation of a cell when the cell becomes completely insensitive to subsequent stimuli

relative refractory period

second part of the refractory period. period following stimulation of a cell when the cell becomes partially insensitive to subsequent stimuli

what are the two types of synapses

electrical and chemical

excitatory postsynaptic potential (EPSP)

depolarization in postsynaptic membrane that brings membrane potential close to the threshold

inhibitory postsynaptic potential (IPSP)

hyperpolarization of the postsynaptic membrane which moves the membrane potential away from the threshold.

neuromodulators

substances released from neurons that influence the likelyhood of an AP being produced in the postsynaptic cell

spatial summation

when multiple AP from separate neurons arrive simultaneously at the same postsynaptic neuron

temporal summation

two or more APs arrive in quick succession at the same postsynaptic cell

serial pathway

input travels along only one pathway

parallel pathway

input travels along several pathways

types of parallel pathway CNS organization

1. convergent

2. divergent

3. reverberating

4. parallel after-discharge

convergent pathway

multiple neurons CONVERGE upon a smaller number of neurons

divergent pathway

a smaller number of neurons synapse with a larger number of neurons

reverberating circuit pathway

create a feedback loop, allows producing an action potential more than once

parallel after-discharge circuit

neurons that stimulate several neurons in a parallel organization which all converge on one output cell