Lecture 13- Nervous Tissue

CNS

Associated with the brain and the spinal cord

PNS

Associated with the all nervous tissues outside the CNS

control and adjust activity of the body, provide brief and swift responses

Main functions of the nervous system

CNS

• Responsible for integrating, processing, and coordinating sensory input

• Responsible for integrating, processing, and coordinating motor output

• it is the seat of intelligence, memory, learning, and emotion

PNS

• Provides sensory information to the CNS and carries motor commands away from the CNS

• Can be divided into afferent & efferent

afferent division of the PNS

– Brings sensory information to the CNS
– Begins at the receptors

efferent division of the PNS

– Carries motor commands to muscles and glands
– Ends at the effectors

sensory information, motor commands

The PNS provides ___________ to the CNS and carries ______________ away from the CNS

Neurons

Nerve cells that are responsible for the transfer and processing of information in the nervous system

• soma (cell body)

• axon

• dendrites

• perikaryon

• dendritic spines

• axon terminals

what makes up a neurons

neuroglia

▪ Supporting cells
▪ Protect the neuron

astrocytes, oligodendrocytes, microglia, ependymal cells

what are the neuroglia of the CNS

astrocytes

-largest and most numerous neuroglia

-make up the blood brain barrier (BBB)

oligodendrocytes

form myelin sheath/form internodes and myelin sheath gaps

white matter

Areas of the CNS with mostly myelinated axons

gray matter

Areas of the CNS without myelinated axons, mostly composed of cell bodies

microglia

phagocytic neuroglia/cells

ependymal cells

• involved in cerebrospinal fluid (CSF) production

  • Make up a cellular lining called the ependyma

ganglia

the cell bodies in the PNS are clustered in ganglia

peripheral nerves

axons are bundled together to form

Satellite cells and schwann cells

neuroglia types found in the PNS

peripheral nerves

in the PNS, Axons are bundled together to form __________

ganglia

The cell bodies in the PNS are clustered in __________

satellite cells

neuroglia that surround cell bodies

schwann cells/neurolemmocytes

neuroglia that surround axons to create myelination

neurolemma

surface of the Schwann cell with the nucleus

axolemma

inner layer of a Schwann cell in direct contact with the axon

nodes (of Ranvier)

areas of axons that are not covered by schwann cells

satellite cells

• surround neuron cell bodies in ganglia

• regulate O2, CO2, nutrient and neurotransmitter levels around neurons in ganglia

Schwann cells

• surround all axons in PNS

• myeline peripheral axons

• participate in repair process after injury

step 1 of myelination

in myelinating a peripheral axon, a Schwann cell first encloses a segment of the axon within a groove of its cytoplasm

step 2 of myelination

the Schwann cell then rotates around the axon

step 3 of myelination

• as the Schwann cell rotates, the inner membranous layers are compressed and the cytoplasm is forced into more superficial layers

• when completed, the myelin sheath consists only of phospholipid bilayers of the plasma membrane w the Schwann cell nucleus and cytoplasm at the surface

• perikaryon

• neurofilaments/neurotubules

• nissil bodies

• axon hillcok

• axoplasm

• collaterals

• telodendria

• axon terminals

• axoplasmic transport

neurons consist of

perikaryon

neuron cytoplasm

neurofilaments or neurotubules

make up the neuron cytoskeleton

nissl bodies

clusters of free ribosomes in a neuron

axon hillock

area where the initial segment connects to the cell body

axoplasm

cytoplasm of the axon

collaterals

branches off the axon

telodendria

ends of the axon and collaterals

axon terminals

ends of the telodendrias

axoplasmic transport

the movement of material between the cell body and the axons

structure or function

neurons can be classified based on

structural classification

based on the # of processes extending from the cell body

functional classification

• sensory

• motor

• interneuron (involved w both sensory and motor)

axonic

– Has many processes but cannot differentiate between axons and dendrites
– Found only in the CNS

Bipolar

-The cell body is between the dendrite and axon
– Axons are not myelinated

pseudounipolar

-The cell body is off to one side of the axon

multipolar

- Typically has a single axon and multiple dendrites
– Most common type in the CNS

sensory (afferent division) neurons

• The axons are afferent fibers

• Sends information from the PNS to the CNS

• somatic and visceral sensory neurons

• 3 categories of receptors

interoroceptors

monitor internal organ activity

exteroceptors

provide information about the external environment

Proprioceptors

monitor position and movement

motor neurons

-The axons are efferent fibers
– Send information from the CNS to the periphery
- consist of 2 divisions

somatic nervous system (SNS)

consists of somatic motor neurons

autonomic nervous system (ANS)

consists of visceral motor neurons, preganglionic fibers, an postganglionic fibers

interneurons

– Located entirely in the CNS
– Situated between the motor and sensory neurons
– Analyze sensory input and coordinate motor output
- can be excitatory or inhibitory

1st step of wallerian degeneration

fragmentation of axon and myelin occurs in distal stump

2nd step of wallerian degeneration

Schwann cells form cord, grow into cut, and unite stumps. Macrophages engulf degenerating axon and myelin

3rd step of wallerian degeneration

axon sends buds into network of Schwann cells and then starts growing along cord of Schwann cells

4th step of wallerian degeneration

axon continues to grow into distal stump and is enfolded by schwann cells

excitability

the ability to conduct the impulse

the axons can, but not cell bodies

can nerves regenerate?

threshold stimulus

the level of stimuli to cause a change in membrane permeability

action potential

a nerve impulse is known as the ____ of a nerve

membrane potential

the uneven distribution of positive and negative ions across the plasma membrane

excitability

The ability to conduct the impulse is known as ____________

propagate

the impulse will ___ the length of the axon

myelin sheath, large diameter of myelinated axons (up to 140 m/s)

what makes impulse speed faster?

lack of myelin sheath, unmyelinated axons w a small diameter (less than 1 m/sec)

what makes impulse speed slower?

synapse

the junction between a neuron and another cell

chemical (vesicular) & electrical (nonvesicular)

2 major types of synapses

true!

T/F: impulses are conveyed in one direction only in chemical synapses

1st step of chemical synapse

an action potential arrives at the presynaptic membrane

2nd step of chemical synapse

this triggers the release of a neurotransmitter from the axon vesicles

3rd step of chemical synapse

the neurotransmitter diffuses across the synapse

4th step of chemical synapse

the neurotransmitter binds to the postsynaptic membrane

5th step of chemical synapse

this binding action causes a change in the permeability of the postsynaptic membrane

6th step of chemical synapse

change in permeability results in an action potential of the next neuron

fasle! impulses can be conveyed in any direction

T/F: impulses are conveyed in only one direction in electrical synapses

1st step of electrical synapse

the presynaptic membrane of one neuron is tightly bound to the postsynaptic membrane of another neuron

2nd step of electrical synapse

this binding permits the passage of ions from one neuron to the next

neuronal pools

Neurons can be organized into smaller organized groups called _______________

neural circuit

the neuronal pools are identified by their ______

• divergence

• convergence

• serial processing

• parallel processing

• reverberation

examples of neural circuits

divergence

• The spread of information from one neuron to several neurons

• permits broad distribution of a specific input

• information enters the CNS and then spreads to the brain and spinal cord at the same time

convergence

• information going from several neurons to a single neuron

• convergence of neurons form rods in the retina of an eye

serial processing

• Information going from one neuron to the next in a sequence

• information going to one part of the brain, then to another, then to another, etc.

parallel processing

• Several neurons are processing the information at the same time

• if you step on a nail, you typically move your foot, shot “ouch” and dance a bit, all at the same time

reverberation

Collateral axons extend back toward the origin of the impulse to cause an enhancement or a continuation of the impulse

divergence!

which neural circuit am I?
a circuit for spreading stimulation to multiple neurons or neuronal pools in the CNS

convergence!

which neural circuit am I?
a circuit for providing input to a single neuron from multiple sources

serial processing!

which neural circuit am I?
a circuit in which neurons or pools work sequentially

parallel processing!

which neural circuit am I?
a circuit in which neurons or pools process the same information simultaneously

reverberation

which neural circuit am I?
a positive feedback circuit

neurons in the PNS

• consist of ganglia

• axons are bundled together in nerves

neurons in CNS

• collection of cell bodies called a center

• if this center has a distance boundary, it is called a nucleus

• white matter consists of axons in bundles called tracts and columns

• proprioceptors

Which of the following structures are receptors that monitor the position and movement of skeletal muscles and joints?
• exteroceptors
• interoceptors
• proprioceptors
• neuroeffectors

• afferent division of the peripheral nervous system

Which of the following carries
sensory information to the central
nervous system?
• efferent division of the peripheral nervous system
• afferent division of the peripheral nervous system
• somatic nervous system
• autonomic nervous system