chapter 10 - Neural Tissue

Question 1

Neuroglial cells

aka Neuroglia

Answer 1

conduct phagocytosis

fill spaces

produce components of myelin

provide structural frameworks

Question 2

can Neuroglia divide

Answer 2

yes

Question 3

can Neurons divide

Answer 3

no

they are amitotic, loosing their ability to divide

Question 4

types of Neuroglia

Answer 4

astrocytes
ependymal cells
microglial cells
oligodendrocytes

in the PNS the two types of neuroglia are -
satellite cells
schwann cells

Question 5

what does the nervous system do

Answer 5

controls body functions
maintains homeostasis
allows the body to respond to many varieties of changing conditions

Question 6

how does the Nervous System (NS) work

Answer 6

information is carried to the brain and spinal cord, which then stimulate the bodies responses.

there are millions of sensory receptors that monitor changes (sensory input) outside and inside the body. The NS processes and interprets this information to determine how it should react (integration)

Question 7

what are effector organs

Answer 7

muscles and glands that are activated by the NS to respond. The responses are collectively termed ‘motor output’

Question 8

CNS consists of

Answer 8

brain and spinal cord, located in the dorsal cavity.

Question 9

the Central Nervous System (CNS) is

Answer 9

the control centre of the NS, integrating all its activities.

Reflexes, past happenings and current conditions determine how it will interpret ‘sensory input’ and control ‘motor output’

Question 10

the Peripheral Nervous System (PNS) is

Answer 10

the peripheral nerves connecting the CNS to other parts of the body.

primarily it is made up of nerves extending from the brain and spinal cord to the rest of the body.

The cranial nerves transmit impulses to and from the brain.

The spinal nerves transmit impulses to and from the spinal cord.

Question 11

subdivisions of the PNS

Answer 11

afferent (sensory) division - carries impulses towards the CNS from the body’s sensory receptors.

efferent (motor) division - carries impulses form the CNS to the effector organs. Activating muscles to contract and glands to secrete. They affect (cause) motor response

Question 12

Afferent (sensory) division

Answer 12

Somatic sensory fibres - transmit impulses form the joints, skeletal muscles and skin

Visceral sensory fibres - transmit impulses form visceral organs located in the ventral cavity

The afferent division informs the CNS of all events happening inside and outside the body.

Question 13

Efferent (motor) division

Answer 13

Somatic Nervous System (SNS) - made up of somatic motor fibres transmitting impulses from the CNS to the skeletal muscle. Also called the Voluntary Nervous System because our skeletal muscles are under conscious control. However the SNS also controls involuntary contractions, such as those involved in reflexes.

Autonomic Nervous System (ANS) - contains visceral motor nerve fibres regulating glandular, cardiac and smooth muscle activity. In general the ANS is not under conscious control and is known as the Involuntary Nervous System.

Question 14

two subdivisions of ANS

Answer 14

Sympathetic
Parasympathetic

Their actions usually oppose each other. When one division causes stimulation the other inhibits its actions

Question 15

functions of the nervous system - sensory receptors

Answer 15

sensory receptors at the ends of the peripheral neurons provide the NS sensory functions.

detect changes in the body’s internal and external environment, and relay information. could involve oxygen levels, temperature, light, sound and many other types of information.

the information is converted into nerve impulses which are integrated so they can be processed to achieve the correct reaction.

Motor functions then act on the integrated information.

Question 16

functions of the nervous system - effectors

Answer 16

Response structures called effectors are located outside the NS. When stimulated by nerve impulses these effectors, which include muscles and glands, may contract, secrete or perform other reactive functions.

Consciously controlled functions are handled by the ‘somatic nervous system’ (SNS) which controls the skeletal muscle.

Involuntary effectors such as the heart, various glands and smooth muscle in blood vessels are controlled by the ANS.

The NS helps maintain homeostasis by using its different divisions to respond to changes that occur

Question 17

whats a neuron

Answer 17

neurons are nerve cells. They are the structural units of the nervous system.

The have a cell body or ‘soma’, dendrites and an axon

Dendrites receive electrochemical messages

Axons send out electrochemical messages

dendrite, soma, axon, axon terminals/terminal boutons

Question 18

what do neuroglial cells provide to neurons

Answer 18

insulation
physical support
nutrients

neurons require a continuous, abundant oxygen and glucose supply because they have a very high metabolic rate.

Question 19

structure of a neuron - cell body

Answer 19

the cell body is made up of a cell membrane, a granular cytoplasm and organelles.

organelles in neurons are - lysosomes, Golgi apparatus, mitochondria and neurofibrils.

the cell body is where most biosynthesis occurs in the neuron. Therefore it contains organelles that synthesise chemicals such as proteins.

throughout the cytoplasm is ‘chromatophillic substance’, similar to the ‘rough endoplasmic reticulum’ of other cells. Attached ribosomes synthesise protein.

to maintain cell integrity and shape microtubules and neurofibrils form a structural network.

the centre of the cell has a large round nucleus containing a nucleolus surrounded by cytoplasm.

Question 20

nuclei and ganglia

Answer 20

nuclei are clusters of cell bodies in the CNS

ganglia are clusters of cell bodies in the PNS

Question 21

major subdivisions of nervous system

Answer 21

CNS and PNS

PNS - Sensory function & Motor functions

Motor functions - Somatic nervous system (skeletal muscle effectors) & Autonomic nervous system (smooth muscle, cardiac muscle and gland effectors)

ANS - Sympathetic (fight or flight) & Parasympathetic (rest and digest)

Question 22

processes of neurons

Answer 22

all neuron cell bodies have processes that extend outward. The CNS contains both neuron cell bodies and processes, whereas the PNS mostly contains just processes.

bundles of neuron processes are called ‘tracts’ in the CNS and ‘nerves’ in the PNS

two types of neuron processes - dendrites and axons

Question 23

Dendrites

Answer 23

have multiple branches that act as the neurons main receptive surfaces.

they are the primary receptive regions of neurons, having a large surface area for receiving neuronal signals.

the dendrites convey messages coming towards the cell body. the messages are short distance ‘graded potentials’ instead of long distance ‘action potentials’.

Question 24

Axons

Answer 24

can be myelinated or unmyelinated

Most neurons have a single axon arising form the cell body.

some neurons have short axons and others long axons called nerve fibers.

larger axons are enclosed in myelin sheaths that originate form schwann cells.

some axons have occasional branches known as axon collaterals, which extend at right angles.

has profuse branching at its end known as ‘terminal branches’. the distal ending of these are knob-like and are called ‘axon terminals/terminal boutons/synaptic knobs’

Question 25

schwann cells

Answer 25

The areas of the schwann cells containing most of the cytoplasm and nuclei are located outside the myelin sheath, comprising a ‘neurolemma’.

form myelin sheaths

Question 26

nodes of ranvier

Answer 26

the narrow gaps between the myelin sheaths. 1mm long. occurring at regular intervals

Question 27

internodes

Answer 27

the large areas of myelinated axons. 1-2mm long.

Question 28

myelin

Answer 28

electrically insulates fibers and protects them, increasing their transmission speed of nerve impulses

Question 29

synaptic transmission

Answer 29

occurs in one direction, carried by biochemical called neurotransmitters.

When a nerve impulse reaches the synaptic knob, the synaptic vesicles release a neurotransmitter. it diffuses across the cleft to react with certain receptors on the postsynaptic neuron membrane, either exciting or inhibiting a postsynaptic cell. This depends on the combined effect of excitory and inhibitory inputs from a single (or many) presynaptic neurons.

Question 30

what is a synapse

Answer 30

a junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter

Question 31

events that occur at a chemical synapse

Answer 31

chemical synapses allow the release and reception of chemical neurotransmitters. They are more common than electrical synapses and are usually made up of two parts: the axon terminal and a neurotransmitter receptor region.

the axon terminal is a knob like structure of the pre synaptic neuron. The axon terminal contains many synaptic vesicles containing neurotransmitters.

The electrical current from the pre synaptic neuron dissipates into the synaptic cleft. Therefore chemical synapses prevent nerve impulses being directly transmitted between neurons.

Question 32

Major types of neurotransmitters

Answer 32

Acetylcholine
Amino acids (GABA, glutamic acid)
Monoamines (dopamine, histamine, norepinephrine, serotonin)
Neuropeptides (endorphins, enkephalins, substance P)
Gases (nitric oxide)

Question 33

What is an action potential

Answer 33

An action potential is the basis for a nerve impulse.

It is based on the cell membrane reaching its threshold potential, and is a brief reversal of membrane potential with a change in voltage of 100mv

Question 34

Classifications of nerve fibers

Answer 34

They are classified by their diameter, degree of myelination, and speed of conduction.

Group A fibers mostly serve joints, skeletal muscles and skin. They are primarily somatic sensory and motor fibers, with the largest diameter of all types of fibers and thick myelin sheaths. These fibers conduct impulses at speeds as high as 300mph.

Group be fibers are of intermediate diameter, with light myelination. They conduct impulses at speeds averaging approx. 20mph.

Group C fibers are non-myelinated, with the smallest diameter, and cannot create saltatory conduction. They conduct impulses at 2mph or less.