ANAT 3001 nervous tissue

function of nervous system

• gather information from stimuli by sensory receptors

• process the information

• produce a response by activating effector organs (muscles or glands)

structural parts of the nervous system

CNS

• brain

• spinal cord 

• integrating and command center of NS

PNS

• cranial nerves

• spinal nerves

• ganglia

• mostly nerves that carry signals to and from CNS

systems of the nervous system

• sensory: receives sensory information

• motor: carries signals to muscles and glands

sensory system

somatic

• sensations on the skin of the body wall (touch pain, pressure, pulled muscle)

• proprioception (position of body in space)

• special senses (hearing, vision, taste)

visceral (automatic)

• sense stimuli from viscera (internal organs) such as stretch, pain, temperature, blood concentrations

motor system

somatic

• generally voluntary 

• stimulates contraction of skeletal muscles

visceral

• generally voluntary

• stimulates contraction smooth and cardiac muscles, secretion by glands

nervous tissue cells

• neurons

• glial cells

neurons

excitable cells, transmit signal

glial cells

non excitable, support neurons

characteristics of neurons

• conduct electrical signals along plasma membrane

• extreme longevity

• do not divide

• high metabolic rate

neuron = nerve cell = nerve fiber

basic features of a neuron

• dendrites

  • processes that receive impulses and send it towards cell body

• cell body

  • contains nucleus and cytoplasm

• axon

  • process that carries impulse away from cell body

neuron communication

• neurons communicate through a synapse - pass information

• presynaptic neuron

  • release neurotransmitters (chemical messengers) from axon

• postsynaptic neuron

  • neurotransmitters bind to postsynaptic membrane

structural classifications of neurons

• multipolar

• unipolar

• bipolar

multipolar 

• many processes extend from cell body

• many dendrites, one axon

• most abundant (99% of neurons)

unipolar

• one process from cell body that divides into 2 processes

• peripheral process carries sensory info from skin to cell body

• central process travels to the CNS

bipolar

• 2 processes extend from cell body

• very rare

• some special sensory organs (inner ear, olfactory, retina)

functional classifications of neurons

• sensory neurons (afferent)

• interneuron

• motor neurons (efferent)

sensory neurons (afferent)

• transmit impulse toward CNS from receptors in PNS

• most are unipolar with ganglia outside CNS

• central process terminates in CNS

interneuron

• between sensory and motor neurons

• multipolar neurons within the CNS

• 99.98% of all neurons

motor neurons (efferent)

• transmit impulse away from CNS

• multipolar

• cell body in CNS with axon synapsing on target organ

gray and white matter in CNS

brain and spinal cord have distinct gray and white matter that vary by contents

gray matter

butterfly shaped central region

• posterior wing is dorsal horn, anterior wing is ventral horn

• contains cell bodies, dendrites, and nonmyelinated axons

white matter

surround the gray matter

• contains myelinated axons (myelin sheaths give white color)

• axons ascent or descent spinal cord to carry impulses to different parts of CNS

basic spinal cord circuit

reflexes

• reflex arc

• monosynaptic reflex

• polysynaptic reflex

reflex arc

simple chain of neurons that causes simplest reflexive behaviors

• information is not processes by brain before response

monosynaptic reflex

• simplest reflex

• sensory neuron synapses with motor neuron (no interneuron)

• ex: knee jerk flex

polysynaptic reflex

• more common

• one or more interneurons

• ex: withdrawal reflex

nerve

rope like organ of PNS

neuron

single impulse conducting cell

nerve vs neuron

• a nerve consists of many axons or neurons

• a nerve can carry axons of 

  • motor neurons only

  • sensory neurons only

  • both sensory and motor neurons

• many axons are bundles together as fascicles, many fascicles make up a nerve (remember muscle tissue!!)

glial cells or neuroglia

support cells in nervous tissue

glial cells in CNS

• astrocytes

• microglial cells

• ependymal cells

• oligodendrocytes

astrocytes

• star shapes, most abundant cell

• radiating ends attach to axons and capillaries

• regulate blood flow in active brain regions

• regulate neurotransmitter levels

microglial cells

• smallest, least abundant cell

• macrophages of CNS

• engulf invading microorganisms and dead neurons

ependymal cells

• form epithelium that lines central cavity of spinal cord and brain (ventricles)

• produces cerebrospinal fluid (CSF)

oligodendrocytes

• processes wrap around axons in CNS

• create an insulating cover (myelin sheath)

• myelin sheaths - increase speed of impulse conduction along axon, more energy efficient

glial cells in PNS

• satellite cells

• schwann cells (neurolemmocytes)

satellite cells

• surround neuron cell bodies within ganglia

• regulate delivery of nutrients and removal of waste from neurons

schwann cells (neurolemmocytes)

• myelinate axons in PNS

• each neurolemmocyte is a single myelin sheath on an axon