chapter 10 - Neural Tissue Flashcards
Neuroglial cells
aka Neuroglia
conduct phagocytosis
fill spaces
produce components of myelin
provide structural frameworks
can Neuroglia divide
yes
can Neurons divide
no
they are amitotic, loosing their ability to divide
types of Neuroglia
astrocytes
ependymal cells
microglial cells
oligodendrocytes
in the PNS the two types of neuroglia are -
satellite cells
schwann cells
what does the nervous system do
controls body functions
maintains homeostasis
allows the body to respond to many varieties of changing conditions
how does the Nervous System (NS) work
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)
what are effector organs
muscles and glands that are activated by the NS to respond. The responses are collectively termed ‘motor output’
CNS consists of
brain and spinal cord, located in the dorsal cavity.
the Central Nervous System (CNS) is
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’
the Peripheral Nervous System (PNS) is
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.
subdivisions of the PNS
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
Afferent (sensory) division
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.
Efferent (motor) division
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.
two subdivisions of ANS
Sympathetic
Parasympathetic
Their actions usually oppose each other. When one division causes stimulation the other inhibits its actions
functions of the nervous system - sensory receptors
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.
functions of the nervous system - effectors
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
whats a neuron
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
what do neuroglial cells provide to neurons
insulation
physical support
nutrients
neurons require a continuous, abundant oxygen and glucose supply because they have a very high metabolic rate.
structure of a neuron - cell body
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.
nuclei and ganglia
nuclei are clusters of cell bodies in the CNS
ganglia are clusters of cell bodies in the PNS
major subdivisions of nervous system
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)
processes of neurons
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
Dendrites
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’.
Axons
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’
schwann cells
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
nodes of ranvier
the narrow gaps between the myelin sheaths. 1mm long. occurring at regular intervals
internodes
the large areas of myelinated axons. 1-2mm long.
myelin
electrically insulates fibers and protects them, increasing their transmission speed of nerve impulses
synaptic transmission
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.
what is a synapse
a junction between two nerve cells, consisting of a minute gap across which impulses pass by diffusion of a neurotransmitter
events that occur at a chemical synapse
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.
Major types of neurotransmitters
Acetylcholine
Amino acids (GABA, glutamic acid)
Monoamines (dopamine, histamine, norepinephrine, serotonin)
Neuropeptides (endorphins, enkephalins, substance P)
Gases (nitric oxide)
What is an action potential
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
Classifications of nerve fibers
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.
