BIOL 1593 Module 9 - Nervous Tissue

What are the 3 basic functions of the nervous system?

sensory, integrative, and motor

What is the sensory function of the nervous system and which neurons serve this function?

to sense changes in the internal and external environment through sensory receptors; sensory neurons

What is the integrative function of the nervous system and which neurons serve this function?

interpret sensory information and determine the appropriate motor response; association neurons (interneurons)

What is the motor function of the nervous system and which neurons serve this function?

initiate acion (i.e. muscle movements or gladular secretions); motor neurons

What 7 items comprise the nervous system?

the brain, cranial nerves, spinal cord, spinal nerves, ganglia, enteric plexus, and sensory receptors

How many pairs of cranial nerves are there and from what part of the skull do they emerge?

12; the foramina, located at the base of the skull

What is a nerve?

a bundle of hundreds or thousands of axons, which courses along a defined path and serves a specific region of the body

Through which part of the skull does the spinal cord connect to the brain?

foramen magnum

How many pairs of nerves emerge from the spinal cord?

31

What are ganglia and where are they located?

clusters of nerve cell bodies that exist outside the CNS

What does the enteric plexuses do?

help to regulate the digestive system

Sensory receptors can be part of which 2 things? And what do they monitor?

neurons or specialised cells; the internal and external environment

What comprises the central nervous system (CNS)?

brain and spinal cord

What comprises the peripheral nervous system (PNS)?

cranial and spinal nerve, which contain sensory (afferent) and motor (efferent) components, ganglia, and sensory receptors

What are the 3 subdivisions of the peripheral nervous system?

somatic (voluntary), autonomic (involuntary), and enteric

What does the somatic nervous system (SNS) consist of?

neurons that conduct impulses from cutaneous and special sense receptors to the CNS, and motor neurons that conduct impulses from the CNS to skeletal muscle tissue

What does the autonomic nervous system (ANS) consist of?

sensory neurons from visceral organs, and motor neurons that convey impulses from the CNS to smooth muscle tissue, cardiac muscle tissue, and glands

What are the 2 subdivisions of the autonomic nervous system?

sympathetic and parasympathetic

What does the enteric nervous system (ENS) consist of?

neurons in the enteric plexuses that extend the length of the gastrointestinal (GI) tract

Many neurons in the enteric plexuses function _________ of the autonomic and central nervous systems.

independently

What do sensory neurons in the enteric nervous system do?

monitor chemical changes within the GI tract and the stretching of its walls

What do motor neurons in the enteric nervous system do?

govern the contraction of GI tract organs, and the activity of the GI tract endocrine cells

What property do neurons have?

electrical excitability

What 3 things do most nerve cells (neurons) consist of?

a cell body, many dentrites, a single axon

What is contained within the cell body of a neuron?

nucleus, lysosomes, mitochondria, a Golgi complex, and rough endoplasmic reticulum (RER)

The rough endoplasmic reticulum (RER) of the neuron is sometimes called...

Nissi bodies

What forms the cytoskeleton of neurons?

neurofibrils

What part of a neuron conducts impulses TO the cell body?

dendrites

What part of a neuron conducts impulses away FROM the cell body?

axon

What is the space between 2 neurons or a neuron and an effector cell?

synapse

What are neuroglia/glia?

specialized tissue cells that support neurons, attach neurons to blood vessels, produce the myelin sheath around axons, and carry out phagocytosis

What are 6 types of neuroglia?

astrocytes, oligodendrocytes, microglia, ependymal cells, Schwann cells, satellite cells

What is the function of astrocytes?

provide support for neurons and maintain the blood-brain barrier; in the CNS

What is the function of oligodendrocytes?

provide myelin insulation for axons in the CNS

What is the function of microglia?

phagocytosis in the CNS

What is the function of ependymal cells?

epithelial cells (often cilliated) that line the ventricles of the brain and produce cerebrospinal fluid (CSF)

What is the function of Shwann cells?

myelin production in the PNS

What is the function of satellite cells?

provides support for neurons in the ganglia in the PNS

What is the myelin sheath?

a multilayer lipid and protein covering produced by the Shwann cells (in the PNS) and oligodendrocytes (in the CNS) that surrounds the axons of most neurons

What is the function of the myelin sheath?

it electrically insulates the axon and increases the conduction speed of nerve impulses

Schwann cells produce the myelin sheath in the _____, whereas the myelin sheath is produced by oligodendrocytes in the _____.

PNS; CNS

What is the sheath of Schwann or neurolemma?

outer nucleated cytoplasmic layer of the Schwann cell, which encloses the myelin sheath

What does the sheath of Shwann do?

it aids in the regeneration of an injured axon by forming a regeneration tube that guides and stimulates the regrowth of the axon

What are the gaps in the myelin sheath called?

nodes of Ranvier

In the CNS, what is white matter?

regions of the nervous system containing mostly myelinated axons (more lipids - whiter color); composed of myelinated and unmyelinated processes

In the CNS, what is grey matter?

regions of the nervous system containing mostly unmyelinated axons; composed of nerve cell bodies, dendrites, and axon terminals or bundles of unmyelinated axons and neuroglia

What is the organisation of grey and white matter in the spinal cord?

grey matter forms an H-shaped inner core and is surrounded by white matter

What is the organisation of grey and white matter in the brain?

a thin outer shell of grey matter covers the cerebral hemispheres

Excitable cells communicate with each other by way of _______ potentials or _______ potentials.

action; graded

How do action and graded potentials differ?

communication: action potentials - both long and short distances, graded potentials- short distances only

Production of potentials depends on the existence on what 2 things?

transmembane polarity/resting membrane potential and certain types of ion channels

What is a membrane potential?

an electrical voltage across the membrane

What is the meaning of resting membrane potential?

the potential difference that exists across a nerve cell membrane when it is not conducting an impulse, usually about -70 millivolts

Potentials can occur because of the movement of what?

ions across the membrane

What are the 2 basic types of ion channels?

leakage/non-gated and gated

How do leakage/non-gated and gated channels differ?

leakage are always open, gated open and close in response to stimulus

What 4 things do gated ion channels respond to?

voltage changes in the membrane potential, specific ligands/chemicals, mechanical vibration, and pressure

The membrane of a non-conducting neuron is _________ outside and ________ inside.

positive; negative

The positive outside and negative inside status of a non-conducting neuron is due to what 2 factors?

the distribution of different ions across the membrane and the relative permeability of the membrane toward Na+ and K+

What is the typical value for the resting membane?

-70 millivolts (mV)

What 2 things determine the resting membrane potential?

the unequal distribution of ions across the plasma membrane, and its selective permeability to Na+ and K+

What compensates for the slow leakage of Na+ into the cell by pumping it back out?

sodium-potassium pumps

What is the role of the sodium-potassium pump (also called Na+/K+ ATPase)?

to actively carries sodium out of the cell and potassium into the cell. It is powered by ATP.

What is an action potential (impulse)?

the depolarization (-70 mV to +30 mV) and then repolarization (+30 mV to -70mV) of the cell membrane; there is also a period of hyperpolarization where the voltage fall below -70 mV before returning to rest

Opening of voltage-gated _____ channels causes depolarization.

Na+

The closing of voltage-gated _____ channels, and the opening of voltage-gated _____ channels causes repolarization.

Na+; K+

What is repolarization?

the recovery of the resting membrane potential

What is the refractory period?

the time an excitable membrane takes to be able to respond to a second stimulus once it has returned to its resting state; during this period another impulse cannot be triggered or a suprathreshold stimulus is required to trigger an impulse

What is an absolute refractory period?

when another impulse cannot be triggered

What is a relative refractory period?

when another impulse can only be triggered by a suprathreshold stimuli

What is a threshold stimulus?

a stimulus that causes the membrane of a neuron to depolarize to a critical level (-55 mV) to generate an action potential

An action potential travels _______ along the membrane.

point to point

What is a travelling action potential?

nerve implulse

What is the all-or-none principle?

if a stimulus is strong enough to generate an action potential, the impulse travels at a constant and maximum strength during the existing conditions; a stronger stimulus does not cause a larger impulse

What is continuous conduction?

the step-by-step depolarization of each adjacent area of the plasma membrane in an umyelinated axon

What is saltatory conduction?

when an impulse jumps from node of Ranvier to node of Ranvier in a myelinated axon; very fast and requires less energy expenditure of the sodium-potassium pump

The propogation speed of a nerve impulse if not related to stimulus strength, but rather to these 3 factors:

fiber diameter (larger = faster), myelination (myelinated = faster), temperature (warm = faster)

What is a neurotransmitter?

a chemical released by a presynaptic neuron for the purpose of stimulating or inhibiting the postsynaptic neuron

A nerve impulse travels from __________ to _________ neurons.

presynaptic; postsynaptic

List the 5 stages of a synaptic event.

1) An impulse arrives at the end bulb of an axon.

2) Calcium channels open on the end bulb, and calcium flows in.

3) Neurotransmitters are released into the synaptic gap.

4) Neurotransmitters bind to postsynaptic receptors and open ion channels.

5) The open ion channels allow other ions to enter, and this process triggers an impulse in the postsynaptic neuron.

Why does the synaptic conduction of an impulse occur only in one direction?

Transmission must be unidirectional because neurotransmitters are released only from presynaptic terminals, and because only postsynaptic membranes have appropriate neurotransmitter receptors.

What are 3 ways that neurotransmitters are removed from the synaptic cleft?

diffusion, enzymatic degradation; and uptake into cells (neurons and glia)

Both ______ and ____ neurotransmitters are present in the pheripheral and central nervous system.

excitatory and inhibitory

The same neurotransmitter can be ____ in one location and ____ in another.

excitatory; inhibitory

Name 8 important neurotransmitters.

acetylcholine, glutamate, aspartate, gamma aminobutyric acid, glycine, norepinephrine, epinephrine, and dopamine

What are 4 ways that neurotransmitters can be modified?

stimulating or inhibiting neurotransmitter synthesis, blocking or enhancing neurotransmitter release, stimulating or inhibiting neurotransmitter removal, and/or blocking or activating the receptor site

What are the 2 classes of neurotransmitters?

small-molecule neurotransmitters and neuropeptides

Name 5 small-molecule neurotransmitters.

acetylcholine, amino acids, biogenic amines, adenosine triphosphate (ATP) and other purines, and gases

What are neuropeptides?

neurotransmitters consisting of amino acids linked by peptide bonds