A&P Ch. 11 Functional Organization of Nervous Tissue

Components of the nervous system

• brain

• spinal cord

• nerves

• sensory receptors

2 main cell types of nervous system

neurons and glial cells

neurons

• functional cells

• electrically excitable

• body with several processes

nerve

collection of many axons bundled together outside of brain and spinal cord

how many pairs of cranial nerves are there

12

how many pairs of spinal nerves are there

31

ganglia

• neurons that form clusters of cell bodies outside of brain and spinal cord

• knot-like swelling in nerve where cell bodies are found

Nervous system/Glial cell functions (5)

1. maintaining homeostasis

2. receiving sensory input

3. integrating information

4. controlling muscles and glands

5. establishing and maintaining mental activity

Major divisions of nervous system

Central and peripheral

• communicate with each other to maintain homeostasis

CNS functions

• decision maker

• receives information from body and sends information to body

PNS functions

• detects stimuli in and around body

• sends stimuli information to CNS

• communicates messages from CNS to body

CNS components

brain and spinal cord

PNS components

all nervous tissue outside of CNS: nerves, ganglia, sensory receptors

PNS Divisions

• sensory (afferent)

• motor (efferent)

Sensory division function

transmits electrical signals from specialized receptors in body towards CNS

Motor division function

transmits electrical signals from CNS to effector organs

Branches of PNS motor division

• Somatic (voluntary- skeletal muscles)

• Autonomic (involuntary- heart, glands, smooth muscle)

Divisions of PNS autonomic branch

sympathetic and parasympathetic

Sympathetic division functions

readies body for activity (fight or flight)

Parasympathetic division functions

regulates resting functions (rest and digest)

Parts of a neuron

• cell body (soma)

  • Nissl bodies (rough ER)

• Dendrites

  • extension of cell body

• axons

  • arise from axon hillock part of cell body

trigger zone

• where axon potentials are generated

• formed from axon hillock and initial segment of axon

anterograde

movement away from cell body

retrograde

movement towards cell body

structural categories of neurons

• multipolar: many dendrites, single axon

• bipolar: one dendrite, one axon

• pseudo-unipolar: start as bipolar during development, but two processes fuse into one axon

• anaxonic: no axons, only dendrites

CNS glial cell types

• astrocytes

• Ependymal cells

• Microglia

• Ogliodendrocytes

PNS glial cells

• Schwann cells/neurolemmocyte

• Satellite cells

White matter

• myelinated axons

• deep to cortex

Nerve tracts

white matter of CNS, propagate action potentials

Gray matter

• groups of cell bodies, dendrites, glial cells

• little myelin

• integrative functions

Cortex

• CNS

• consists of gray matter on surface of brain and nuclei deeper in brain

nuclei

clusters of of neuron cell bodies in gray matter

Cation ionic permeability characteristics

Na+ wants to leak in and K+ wants to leak out

Ion with major influence on resting membrane potential

Potassium

Proportional to tendency for K+ to diffuse out of cell

cytoplasm electrical charge

neutral

Graded potential characteristics

• variable strength proportional to stimulus

• small change in potential localized to one area of membrane

• Decremental: decrease in magnitude as they spread

• Summation: can add together to result in action potential

Action potential characteristics

• result from summation of graded potentials at axon hillock trigger zone

• all or nothing

• propagates without changing in magnitude

4 phases of an action potential

1. depolarization

2. repolarization

3. afterpotential

4. return to resting

takes 1-2 milliseconds to occur

Refractory period

once an action potential is produced, that section of the plasma membrane becomes less sensitive to further stimulation

1. absolute refractory period

2. relative refractory period

electrical synapses

• between cells connected at gap junctions

  • cytoplasm shared through connexins

• in cardiac and smooth muscle

Excitatory postsynaptic potential (EPSP)

when depolarization occurs and response is stimulatory, causing a graded potential

parallel after-discharge circuits

• neurons that stimulate several neurons in parallel organization that all converge upon common output cell

• involved in complex neuronal processes and intricate functions