Chapter 11: Fundamentals of the Nervous System and Nervous Tissue

functions of the nervous system

gathers sensory input, integrates sensory input, causes response or motor output

histology of nervous tissue

• supporting cells:

  • “nerve glue”

  • surrounded and wrap neurons

  • called neuroglia or glial cells

• neurons:

  • excitable nerve cells that transmit electrical signals

supporting cells in the CNS

astrocytes, microglia, ependymal cells, oligodendrocytes

astrocytes

star-shaped, most abundant glial cell, support neurons (anchor them to capillaries), mop up leaked K+, recycle neurotransmitters

microglia

transform into a microphage (phagocytize neuronal debris, microorganisms)

ependymal cells

line central cavities of brain and spinal cord, beat their cilia to circulate CSF

oligodendrocytes

line up along thicker CNS neurons and wrap them with cytoplasmic extension, produce insulating covers called myelin sheaths

supporting cells in the PNS

satellite cells and schwann cells

satellite cells

surround neuron cell bodies within ganglia and function unknown

schwann cells

surround and form myelin sheaths around large fibers of PNS and vital for peripheral nerve fiber regeneration

neurons

the structural units of the nervous system

functions of neurons

conduct messages (nerve impulses), extreme longevity, amitotic, and high metabolic rate

parts of a neuron: the cell body

biosynthetic center: rough ER most active of any cell, no centrioles. plasma membrane of cell body receives info from other neurons. most cell bodies within CNS. clusters of cell bodies in CNS=nuclei. cell bodies that lie along nerve in PNS=ganglia

tracts

bundles of neuron processes in the CNS

nerves

bundles of neuron processes in the PNS

dendrites and axons

two types of neuron processes

dendrites

branching, receptive or input region. large surface area to synapse with other neurons. convey incoming short-distance signals (graded potentials) toward the cell body

axon

generates and transmits nerve impulses away from cell body. each neuron has single axon (long axon called nerve fiber). terminal branches have endings called synaptic knobs (boutons) release neurotransmitters.

myelin sheath and neurilemma

whitish, fatty segmented sheath (covers nerve fibers especially long or large fibers). protects. electrically insulates fibers from one another. increases speed of nerve impulse (150x over unmyelinated fiber)

myelin sheath formation in PNS

formed by Schwann cells (wrap around axon in “jelly roll fashion”. adjacent Schwann cells along axon don’t touch: gaps in sheath called nodes of Ranvier

PNS peripheral nervous system

central nerves and spinal nerves, communication lines between the CNS and the rest of the body

2 branches of PNS

sensory (afferent) division and motor (efferent) division

motor (efferent) division

motor nerve fibers, conducts impulses from the CNS to effectors (muscles and glands)

2 branches of motor (efferent) division

somatic nervous system and autonomic nervous system

somatic nervous system

somatic (voluntary) motor nerve fibers, conducts impulses from the CNS to skeletal muscles

autonomic nervous system (ANS)

visceral (involuntary) motor nerve fibers, conducts impulses from the CNS to cardiac muscles, smooth muscle, and glands

2 branches of ANS

sympathetic division, parasympathetic division

sympathetic division

mobilizes body systems during activity

parasympathetic division

conserves energy, promotes housekeeping functions during rest

neuron diagram

1. dendrites

2. cell body

3. nucleus

4. nucleolus

5. chromatophilic substance (rough ER)

6. initial segment of axon

7. axon hillock

8. impulse direction

9. Schwann cell

10. terminal branches

11. myelin sheath gap

12. axon terminals (secretory region)

13. axon (impulse-generating and conducting region)

myelin sheath and neurilemma

whitish, fatty segmented sheath: covers nerve fibers, especially long or large fibers

protects

eclectically insulates fibers from one another

increases speed of nerve impulse (150x over unmyelinated fiber)

classification of neurons

structural: multipolar, bipolar, unipolar

multipolar neurons

three of more process, 99% of neurons in this class

bipolar

rare, two processes- axon and dendrites; receptors of retina, olfactory mucosa

unipolar

single, short process that divides T-like into proximal and distal branches

functional classification of neurons

direction nerve impulse travels relative to CNS

sensory (afferent)

from skin/internal organs toward CNS

motor (efferent)

carry impulses away from CNS to the effector organs (muscles and glands), usually cell bodies in CNS, usually multipolar

interneurons (association neurons)

lie between motor and sensory neurons, shuttle signals through CNS, often multipolar, 99% of neurons in body

neurophysiology

neuron stimulated, electrical impulse (action potential) conducted along length of axon; separated electrical charges of opposite sign have potential energy: for example- stored potential energy of battery, complete circuit, allow negatively charged electrons to flow to positive area, energy released

voltage

measure of potential energy generated by separates charge, volts or millivolt (mV), measured between two points

current

flow of electrical charge from one point to another, used to do work, current flow in body by ions

resistance

hindrance to charge flow, insulators (high electrical resistance), conductors (low resistance), plasma membrane provides resistance to current flow

Ohm’s law

current (I)= voltage (V)/resistance (R)

operation of gated channels

gating mechanisms

chemically gated ion channels

open in response to binding of the appropriate neurotransmitter

voltage-gated ion channels

open in response to changes in membrane potential