Chapter 11 (unit 1) A&P II

Nervous system does what three things?

• Help detect environment (sensory input: information gathered by sensory receptors about internal and external changes)

• Integration: interpretation of sensory input (complex vs simple integration)

• Motor output: activation of effector organs (muscles and glands) produces a response

What comprises the nervous system?

• Afferent: towards central nervous system

• Efferent: to move away from the central nervous system (always motor, can be voluntary or involuntary)

• Somatic nervous system: voluntary nervous system: ex: used in order to write things down, targets skeletal muscle

• Visceral motor: (involuntary)

• Autonomic: operates below levels of consciousness (true for entire body, regulates blood pressure and vessels, secretion of hormones, digestion, pupils, sweating, etc)

• Parasympathetic division: regulate a lot of processes below levels on consciousness, inhibits heart rate

• Sympathetic division: regulate a lot of processes below levels on consciousness, flight or fight, increases heart rate excites it

• Some nervous system activity is inhibitory: exerted yourself, heart rate is elevated, heart rate slows down once you sit, this is bc nervous system is inhibiting heart rate

Histology of nervous tissue

• Two principal cell types in the nervous system
  1. Neuroglia (glial cells)- supporting cells, support function for neurons and protects them

2. Neurons: excitable cells that transmit information at synapses signals

Astrocyte

• Only found in central nervous system:

• Most abundant,versatile, and highly branched glial cells

• Cling to neurons, synaptic endings, and capillaries

• Support and brace neurons

• Help determine capillary permeability

• Regulate capillaries that supply the rest of the nervous system to get or restrict nutrients, they allow the capillaries to open or close, prevents pathogens from accessing the nervous system

Microglia

• Only found in central nervous system

• move towards site of injury and promote localized inflammation

• Small, ovoid cells with thorny processes

• Migrate toward injured neurons

• Phagocytize microorganisms and neuronal debris

Ependymal Cells

• Range in chape from squamous to columnar, may be ciliated

• Line the central cavities of the brain and spinal cord

• Separate the CNS interstitial fluid from cerebrospinal fluid

• Produce CSF at choroid plexus

• Depending on their function, they have different features

Oligodendrocytes

• Produce myelin in the cns

• Processes wrap around multiple axons in CNS forming undulating myelin sheaths

• Multiple sclerosis (demyelation of CNS)

• Speeds up rate at which information is communicated

• Schwann cells are like this but not in CNS

Satellite Cells

• Equivalent of astrocyte just in PNS

• Surround neuron bodies in PNS

• Regulate blood flow to cells

Schwann Cells: (neurolemmoncytes)

• In PNS, to speed up rate in which information is communicated in the PNS

• Most common neuron is the multipolar neuron then the unipolar neuron (pseudo unipolar) then bipolar

• Trigger zone varies depending upon type of cell we are looking at
  - multipolar: trigger zone right next to the soma (cell body)

• Unipolar: trigger zone is next to dendritic endings

• Bipolar: trigger zone right next to next to the axon hillock and just before the start of the first myelin-forming glial cell

Multipolar Neuron

• Every neuron has a cell body (referred to as soma)

• Surrounding the soma is dendrites (region of neuron that receives information from other sources- feeling something at fingertips is receptors associated with dendrites)

• Both soma and dendrites are receptive regions of multipolar cell, dendrites just have more surface area

• Axon: extends off of soma

• Axon pilla: where axon interfaces with soma, generates activation potential

• Axonal branches: branches off of axon

• Boutons (axonal terminals): end of axon branches

• Neurons can form relationships with other type of cells such as skeletal muscle and glands

• Synapse: presynaptic neuron forms relationship with target cell or post synaptic neuron

Neural Pathways: Spinocerebellar (SC)

Neural Pathways: Dorsal Column–Medial Lemniscus (DCML)

Neural Pathways: Spinothalamic (ST)

Lateral corticospinal (pyramidal) pathway

What would happen if a patient has a partial injury to spinal cord between cervical and lumbar, either on the right or left side?

They won’t loose spinal thalamic pathway on left side of body

White Matter

- has myelin
- dense collection of myelinated axons
- myelin is specifically associated with axons
- when talking about white matter, we are talking about axons
- myelin is used to speed up the conduction of action potentials from the axon hillock to boutons
- when we see myelin we have insulator (no channels in membrane)

Gray Matter

- mostly neuron cell bodies and dendrites
- may contain unmyelinated axons
- where we see exposed membrane (nodes of ranvier), it has lots of channels