Unit 19 - Nervous System pt. 1 (Overview and histology)

- central nervous system (CNS)

- peripheral nervous system (PNS)

—  “command centre”

—  brain and spinal cord

—  processes and integrates info

- cranial nerves: to/from brain

- spinal nerves: to/from spinal cord

- sensory/afferent division

- motor/efferent division

afferent: info from the body coming to central nervous system

efferent: info from the central nervous system to body, to initiate action

—  has sensory receptors that detect stimuli (change in internal or external environments)

—  nerves convey impulses away from CNS

—  innervates (supplies nerves to) effectors = muscles and glands (endocrine or exocrine)

Neurons and neuroglia (glial cells)

—  conduct impulses

—  make up CNS and PNS

—  mostly amitotic (irreplaceable)

o   exceptions = taste, olfaction, memory

—  typical organelles

—  RER called -  Nissl Bodies

—  groups/clusters in CNS = nuclei (gray matter)

—  groups/clusters in PNS = ganglia

dendrites and axon

—  receive incoming messages and relay to cell body

—  carry impulses away from cell body

—  axon hillock = where axon meets cell body

—  axon terminal = typically branched with synaptic end bulbs (enlarged tips)

- they may be myelinated or unmyelinated (just no myelin)

- myelinated - – wrapped in many layers of cell membrane from Schwann cells (PNS) or oligodendrocytes (CNS)

- myelinated axon bundles in:

o   CNS = tracts (white matter)

o   PNS = nerves

- electrical insulation

- gaps in myelin sheath are called Nodes of Ranvier

—  support neuron cells = can undergo mitosis (prone to cancer – brain tumor)

- CNS neuroglia

- PNS neuroglia

oligodendrocytes, microglia, astrocytes, and ependymal (neural epithelia)

—  produce myelin around axon

—  protective – become phagocytic if detect infected, dead, or damaged neurons (because immune cells can’t enter CNS)

—  surround blood capillaries to form part of blood brain barrier (BBB)

—  help control capillary permeability

—  line brain ventricles and central canal of the spinal cord

—  secrete cerebrospinal fluid (CSF) and circulate it (cilia)

- Schwann cells: form myelin around axons in PNS

- Satellite cells: surround neuron cell bodies in ganglia – protection and support

Structural/Anatomical types and Functional types

- based on # of cell processes off of cell body

- Unipolar, Bipolar, and Multipolar

—  1 process that divides into two: central and peripheral

—  peripheral end has dendrites = sensory receptors (pain, touch etc) - remainder is axon

—  always sensory

—  2 processes: 1 axon, 1 process with dendrites

—  sensory – retina, nose (olfaction)

—  3 or more processes: 1 axon, many dendrites

—  all interneurons and motor neurons

- based on direction of impulse conduction

- types: Sensory/Afferent Neurons, Interneurons, Motor/Efferent Neurons

—  mostly unipolar

—  from sensory receptors to CNS

- within CNS (between sensory and motor)

- 99% of neurons (mostly multipolar)

- CNS to effectors (all multipolar)

- effectors are parts of the body that respond to stimuli (muscles, glands, etc)

1)     Neuronal junction:

2)     Neuromuscular junction:

3)     Neuroglandular junction:

—  neuron to neuron

—  can be chemical (use neurotransmitters) or electrical (ions)

—  motor neuron to skeletal muscle

—  motor neuron to gland

- the most common neuron junction

- a structure of: Presynaptic Neuron, Axon Terminal, Synaptic Cleft, Postsynaptic Neuron

—  neuron bringing impulse

—  within synaptic end bulbs

o   inside the end bulb (presynaptic membrane) = synaptic vesicles containing neurotransmitter (nt)

—  space between neurons

—  receives the impulse

—  has postsynaptic membrane, which is a cell membrane of dendrites or cell body with receptor sites for nt

- neuromuscular junction