PHYL 141 Nervous Tissue Part 1 (Exam 3 Study Guide)

central nervous system (CNS)

consists of the brain and spinal cord

peripheral nervous system (PNS)

consists of all other nervous tissue outside of the CNS (e.g. peripheral nerves, cranial nerves, spinal nerves)

afferent and efferent division

2 divisions of PNS

afferent division

brings sensory information to the CNS from receptors in peripheral tissues and organs

efferent division

carries motor commands from the CNS to effectors (muscles, glands, and adipose tissue)

receptors

sensory structures that...
- detect changes in environment (internal and external)
- respond to stimuli

somatic nervous system (SNS)

part of the efferent division (PNS) that controls the skeletal muscles (voluntary and involuntary)

involuntary (contractions)

skeletal muscle movements that are controlled at the subconscious level (not aware)

voluntary (contractions)

skeletal muscle movements that are under conscious control (aware)

motor unit

a motor neuron and all the muscle fibers that it innervates

autonomic nervous system (ANS)

part of the efferent division (PNS) that automatically regulates internal organs (smooth muscle, cardiac muscle, glandular secretions, adipose tissue) at a subconscious level

parasympathetic and sympathetic

two divisions of the autonomic nervous system (efferent division of the PNS)

enteric nervous system (ENS)

- an extensive network of neurons and nerve networks in the walls of the digestive tract

- coordinates visceral reflexes locally (without instructions from the CNS)

neuron

a nerve cell; the basic building block of the nervous system

anatomy of a neuron

- cell body
- dendrites
- axons
- telodendria

cell body (neuron)

contains nucleus, organelles, and perikaryon (neuron cytoplasm)

cell body (neuron)

gives nervous tissue its grey appearance (grey matter)

dendrites

branch out from the cell body; play a role in intercellular communication

axon

a long cytoplasmic process that transmits electrical impulses (action potentials)

axolemma

plasma membrane of an axon

axon hillock

connects the cell body to the initial segment of the axon

telodendria

fine terminal extensions at the end of the axon and its collaterals

axon terminals

the end of telodendria; where synapses are located

path of a signal

1. Dendrites receive signals

2. Cell body integrate signals

3. Signals travel through axon

4. Signals reach telodendria

5. Signals are sent to other neurons via the synapses of the axon terminals

anaxonic neurons

- numerous dendrites; no obvious axons

- located in brain and special sense organs

bipolar neurons

- 2 processes: 1 dendrite and 1 axon (cell body in between)

- rare; found in special sense organs

unipolar neurons (pseudounipolar)

- 1 process: dendrite and axon are continuous (cell body balloons to the side)

- sensory neurons usually have this structure (travel to CNS)

multipolar neurons

- multiple processes: 2 or more dendrites and 1 axon

- motor neurons have this structure (travel from CNS)

sensory neuron

- AKA afferent neurons

- usually unipolar

- delivers information from sensory receptors to the CNS (spinal cord or brain)

ganglion

a cluster of neurons in the PNS

nucleus

a cluster of neurons in the CNS

afferent fibers

the processes/axons of sensory neurons

somatic sensory neurons

somatic neurons that monitor the external environment and our positions within it

visceral sensory neurons

somatic neurons that monitor the internal environment and the status of other organ systems

sensory receptor types

1. interoceptors
2. exteroceptors
3. proprioceptors

interoceptors

sensory receptors that monitor internal organ activity (digestive, respiratory, cardiovascular, urinary, and reproductive systems)

exteroceptors

sensory receptors that monitor external stimuli (touch, temperature, pressure, and special senses)

proprioceptors

sensory receptors that monitor the Position and movement of skeletal muscles and joints

motor neuron

- AKA efferent neurons

- carry instructions away from the CNS to effectors (muscle, gland, adipose tissue)

somatic motor neurons

motor neurons that innervate skeletal muscles; use conscious control

visceral motor neurons

motor neurons that innervate smooth muscle, cardiac muscle, glands, and adipose tissue; use no conscious control

CNS neuroglia

astrocytes, oligodendrocytes, microglia, ependymal cells

Dumb mneumonic: MEAO - "meow" for C(at)NS

astrocytes

- most abundant glia

- forms blood brain barrier (BBB)

- repairs damaged nervous tissue

- provides structural and metabolic support

ependymal cells

- line cavities in the CNS

- produce cerebrospinal fluid (CSF)

- their cilia circulates CSF in cavities

oligodendrocytes

- support and myelinate the axons of the CNS

- makes up the fatty, white matter

microglia

- protect against invaders

- dispose of pathogens, debris, and wastes in the CNS (via phagocytosis)

PNS neuroglia

satellite cells, Schwann cells

satellite cells

surround and protect cell bodies of PNS neurons

Schwann cells

- myelinate the axons of the PNS

- the lipid bilayer of this cell wraps around axons to produce myelin

oligodendrocytes, Schwann cells

__________ myelinates the neurons of the CNS, while __________ myelinates the neurons of the PNS.

cerebrospinal fluid (CSF)

basically the same as the plasma from blood but protein-free and clear

cerebrospinal fluid (CSF)

__________ can be found in the central canal, ventricles, and the subarachnoid space surrounding the spinal cord and brain

cerebrospinal fluid (CSF)

__________ is produced when the ependymal cells in the choroid plexus comes in contact with blood vessels and filter and absorb components of blood.

astrocytes, ependymal cells

neuroglia that play an important role in filtration of blood and production of CSF

hydrophobic

Because myelin is lipid-rich (fatty), it is __________. This keeps the axon from being exposed to interstitial fluid.

lipids, proteins

Myelin has __________, which makes it hydrophobic and a good conductor. It also has __________ to hold the glial cell membranes closely together.

oligodendrocytes, Schwann cells

__________ can myelinate multiple axon segments, while __________ can only wrap around only one axon segment.

oligodendrocytes, Schwann cells

For __________, the cell body does not wrap around the axon (only its processes). For __________, the cell body also wraps around the axon.

myelination

the formation of a fatty sheath around the axons of a neuron via certain glial cells

Nodes of Ranvier

Gaps in the myelin sheath that make it easier for impulses to jump from one node to another (signals travel faster)

demyelination

- progressive destruction of myelin sheaths in the CNS and PNS

- results in loss of sensation and motor control

- affected areas are numb and paralyzed