Nervous System, Neurons, and Glia

Neurobiology

the study of the combination of behavioral and life sciences

Endocrine system

Communicates by means of hormones secreted into the blood

Nervous system

Employs electrical and chemical means to send messages from cell to cell

Central Nervous System

Brain and spinal cord, enclosed by cranium and vertebral column

Peripheral Nervous System

Entire nervous system except the brain and spinal cord; composed of nerves and ganglia

Nerve

Bundle of nerve fibers (axons) wrapped in fibrous connective tissue

Ganglion

Knot-like swelling in a nerve where neuron cell bodies are concentrated

Sensory (afferent) division

Somatic and visceral sensory divisions; carries signals from receptors to CNS

Motor (efferent) division

Somatic and visceral motor divisions (sympathetic and parasympathetic); carries signals from CNS to effectors

Somatic sensory division

Carries signals from receptors in the skin, muscles, bones, and joints

Visceral sensory division

Carries signals from the viscera

Somatic motor division

Carries signals to skeletal muscles; output produces muscular contraction and somatic reflexes

Visceral motor division

Carries signals to glands, cardiac, and smooth muscles; involuntary responses are visceral reflexes

Sympathetic division

Fight or flight; accelerated heartbeat/respiration; inhibits digestive and urinary systems

Parasympathetic division

Calming effect; slows heart rate/breathing; stimulates digestive/urinary

Excitability

Respond to environmental changes (stimuli)

Conductivity

Produces electrical signals that travel along nerve fibers (axons) to reach other cells at distant locations

Secretion

Nerve fiber endings (axon terminals) release chemical neurotransmitters that influence other cells

Sensory (afferent) neurons

Detect stimuli and transmit information about them towards the CNS

Interneurons

Lie entirely within the CNS connecting motor and sensory pathways; receive signals from many neurons and carry out integrative functions

Motor (efferent) neurons

Send signals out to muscles and gland cells (effectors)

Soma

Centrally located nucleus with large nucleolus

Axon terminals

Swelling that form contact points (synapses) with other cells

Myelin Sheath

Insulating layer surrounding some axons

Multipolar neuron

One axon and multiple dendrites, most neurons in the CNS

Bipolar neuron

One axon and one dendrite; olfactory cells, retina, and inner ear

Unipolar neuron

Single process leading away from soma; sensory cells from skin and organs to spinal cord

Anaxonic neuron

Many dendrites but no axon; retina, brain, adrenal gland

Axonal transport

Many proteins and peptides made in the soma have to be transported to the axon and terminal

Anterograde transport

Down the axon away from the soma

Retrograde transport

Up the axon toward the soma

Kinesin

Anterograde transport protein

Dynein

Retrograde transport protein

Fast transport

200–400 mm/day

Fast anterograde transport

Organelles, enzymes, synaptic vesicles, and small molecules

Fast retrograde transport

Recycled materials; some pathogens (rabies, herpes, tetanus)

Slow axonal transport

0.2–0.5 mm/day; always anterograde

Neuroglia

Bind neurons together, form supportive tissue framework, cover mature neurons

Oligodendrocytes

Form myelin sheaths in the CNS that speed signal conduction; arm-like processes wrap around nerve fibers

Ependymal cells

Line internal cavities of the brain; secrete and circulate CSF

Microglia

Macrophages; develop from WBCs; concentrated in areas of damage

Astrocytes

Most abundant glia in CNS; covers brain surface and nonsynaptic regions of neurons

Astrocyte functions

Form blood-brain barrier; regulate chemical composition of tissue fluid

2 types of glia in PNS

Schwann cells, satellite cells

Schwann Cells

Wind around the axon, form myelin sheaths, assist in regeneration of damaged fibers

Satellite Cells

Surround the somas of PNS neurons inside ganglia; provide electrical insulation; regulate chemical environment