Fundamentals Of The Nervous System And Nervous Tissue Flashcards
Nervous system
Master controlling and communicating system of the body
Cells communicate via electrical and chemical signals which are rapid and specific- immediate responses
Function of nervous system
Sensory input
Integration
Motor output
Sensory input
info gathered by sensory receptors monitoring changes internally and externally
Integration
processes and interprets sensory input, deciding what should be done at each moment
Motor output
Activates effector (muscles/glands) to cause a response
Central nervous system
Brain and spinal cord
Occupy the dorsal body cavity
Function of CNS
Control centre of nervous system
Interprets sensory input and dictates motor output based on reflexes, current conditions and past experience
Peripheral nervous system
Cranial nerves, spinal nerves and ganglia
Part of the nervous system outside the CNS
Spinal nerves
Carry impulses to and from the spinal cord
Cranial nerves
Carry impulses to and from the brain
What are the functional subdivision of PNS?
Sensory (afferent) division
Motor (efferent) division
Sensory division
Consists of nerve fibres that convey impulses to the CNS from sensory receptors located throughout the body
Keeps CNS constantly informed of events going on both inside and outside of body
Visceral organs
Organs within the ventral body cavity
Somatic sensory fibres
Convey impulses from the skin, skeletal muscles and joints
Visceral sensory fibres
Transmit impulses from the visceral organs
Motor division
Transmits impulses from the CNS to effector organs (muscle/glands)
These impulses activates muscles to contract and glands to secrete
What is the motor division divided into?
Somatic nervous system
Autonomic nervous system
Somatic nervous system
Composed of somatic motor nerve fibres that conduct impulses from the CNS to skeletal muscles
(Voluntary nervous system)
Autonomic nervous system (ANS)
Consists of visceral motor nerve fibres that regulate the activity of smooth muscles, cardiac muscle and glands
(Involuntary nervous system)
What are the functional subdivisions of ANS?
Sympathetic Division
Parasympathetic division
Sympathetic division
Mobilises body systems during activity
Parasympathetic division
Conserves energy
Promotes house keeping functions during rest
What cell types do nervous tissue contain?
Neuroglia (glial cells)
Neurons (nerve cells)
Neuroglia
Small cells that’s surround and wrap the more delicate neurons
Neurons
Nerve cells that’s are excitable and transmit electrical signals
How many types of neuroglia are there?
6
4 in CNS
2 in PNS
What are the neuroglia in the CNS?
Astrocytes
Microglial cells
Ependymal cells
Oligondendrocytes
Astrocytes
Most abundant and versatile glial cells
Cling to neurons and their synaptic endings and capillaries
Function of Astrocytes
Support and brace neurons
Play role in exchanges between capillaries and neurons
Guide migration on young neurons
Control chemical environment around neurons
Respond to nerve impulses and neurotransmitters
Influence neuronal functioning
Participate in information processing in brain
Microglial cells
Small and ovoid with long ‘thorny’ processes that touch and monitor neurons
They migrate towards injured neurons
Can transform to phagocytize microorganisms and neuronal debris
Microglial cells
Small and ovoid with long ‘thorny’ processes that touch and monitor neurons
They migrate towards injured neurons
Can transform to phagocytize microorganisms and neuronal debris
Defensive cells in the CNS
Ependymal cells
Range in shape from squamous to columnar, many ciliated
Line the central cavities of brain and spinal cord, where they form a permeable barrier between the cerebrospinal fluid
Oligondendrocytes
Branched but have fewer processes than Astrocytes
Line up along the thinker nerve fibres in CNS and wrap their processes tightly around the fibres, producing myelin sheath
What are the neuroglia in PNS?
Satellite cells
Schwann cells
Satellite cells
Surround neuron cell bodies located in PNS
Similar function to Astrocytes
Schwann cells
Also called neurolemmocytes
Surround all nerve fibres in PNS and form myelin sheaths around the thicker nerve fibres
Function similar to oligodendrocytes
Vital to regeneration of damaged peripheral nerve fibres
Neurons (nerve cells)
Structural units of nervous system
Large, highly specialised cells that conduct messages in the form of nerve impulses from one part of the body to another
What are the characteristics of neurons?
Extreme longevity- given good nutrition, can function for a lifetime
Amitotic- lose their ability to divide, but some regions of brain contain stem cells which produce new neurons
High metabolic rate- requires continuous supply oxygen and glucose
Neuron cell body
Also known as soma/perikaryon
Consists of spherical nucleus surrounded by cytoplasm
The plasma membrane of the cell body acts as part of the receptive region that receives information from other neurons
Cell body is the biosynthetic Center and metabolic Center of a neuron
Most cell bodies located in CNS, where are protected by the bones of the skill and vertebral column
What structures do neuron cell body contain?
Mitochondria
Protein
Cytoskeletal elements- microtubules and neurofibrils
Pigment inclusions- black melanin, lipofuscin
What is the name for clusters of cell bodies in the CNS?
Nuclei
What is the name for clusters of cell bodies in the PNS?
Ganglia
Neuron processes
Arm like processes extend from the cell body of all neurons
CNS contain both neuron cell bodies and their processes
PNS consists of neuron processes whose cell bodies are in the CNS
What are the types of neuron processes?
Dendrites
Axons
Dendrites of motor neurons
Short, tapering, diffusely branching extensions
They are the main receptive/input region
Provide a large surface area for receiving signals from other neurons
Convey incoming messages toward the cell body
Axon structure
Arises from a cone shaped area of the cell body called axon hillock
Initial segment of axon narrows to form a slender process that is uniform in diameter for the rest of its length
What is a long axon called?
Nerve fibre
Nucleus
A collection of neuron cell bodies in the CNS
Ganglion
A collection of neuron cell bodies in the PNS
Tract
A bundle of axons in the CNS
Nerve
A bundle of axons in the PNS
what is the function of axon?
its the conducting region of the neuron
generates nerve impulses and transmits them, away from cell body along axolemma
Axonal Transport
Axons have efficient internal transport mechanisms
molecules and organelles are moved along axons by motor proteins and cytoskeletal elements
movement occurs in two directions: anterograde + Retrograde
Anterograde movement
movement away cell body
substances moved in this direction- mitochondria, cytoskeletal elements, membrane components, enzymes
Retrograde movement
movement toward the cell body
substances moved in this direction- mostly organelles returning to the cell body to be degraded or recycled, vesicles containing signal molecules
what is responsible for axonal transport?
a single basic bidirectional transport mechanism
uses different ATP dependent motor proteins ( Kinesin/ dynein)
these proteins propel cellular components alone the microtubules
Myelin Sheath
composed of myelin, white protein-lipid substance
function of myelin
protects and electrically insulates fibres
increases the transmission speed of nerve impulses
difference between myelinated and non- myelinated fibres?
myelinated- conduct nerve impulses rapidly
non- myelinated - conduct nerve impulses more slowly
Myelination in the PNS
a Schwann cell envelops an axon
the swchann cell then rotates around the axon, wrapping its plasma membrane loosely around it in successive layers
the Swann cell cytoplasm is forced from between the membranes
the tight membrane wrappings surrounding the axon form the myelin sheath
Nodes of Ranvier
myelin sheath gaps
adjacent swchann cells do not touch one another, so are gas in the sheath
occur at regular intervals along a myelinated axon
axon collaterals can emerge here
Myelination in CNS
CNS contains both myelinated and non- myelinated axons
but oligodendrocytes form myelin sheath in CNS
oligodendrocytes have multiple flat processes that can coil 60 axons at the same time
what are the structural classifications of neurons?
multipolar neurons
bipolar neurons
unipolar neurons
multipolar neurons
3 or more processes
one axon and the rest dendrites
major neuron type in CNS
Bipolar neurons
2 processes
one axon and a dendrite that extend from opposite sides of the cell body
found in retina of eye and in olfactory mucosa
Unipolar neurons
single short processes that emerge from the cell body
also called pseudounipolar neurons
What are the functional classification of neurons?
sensory neurons
motor neurons
interneurons
Sensory neurons
also called afferent neurons
transmit impulses from sensory receptors in internal organs towards CNS
they are unipolar, cell bodies in sensory ganglia outside of CNS
Motor neurons
also known as efferent neurons
carry impulses away from CNS to effector organs
they are multipolar, cell bodies located in CNS
Interneurons
also known as association neurons
lie between motor and sensory neurons in neural pathways and shuttle signals through CNS pathways
voltage gated channels
open and close in response to changes in the membrane potential
Chemical gated channels
open and close in response to binding of the appropriate neurotransmitter
concentration gradient
ions move along from high conc area to low conc area
electrical gradient
ions move toward an area of opposite electrical charge
formula for voltage
voltage = current x resistance
what is the resting membrane potential?
All gated Na+ and K+ channels are closed, and the neuron maintains a resting membrane potential of approximately -70 mV.
What does generating resting membrane potentials depend on?
All gated Na+ and K+ channels are closed, and the neuron maintains a resting membrane potential of approximately -70 mV.
How is the resting membrane potential made?
K+ loss through abundant leakage channels establishes a negative membrane potential
Na+ entry through a few leakage channels reduces the negative membrane potential slightly
Na+ K+ pumps maintain the conc gradients, resulting in resting membrane potential
Depolarisation
decrease in membrane potential
Voltage-gated Na+ channels open, allowing Na+ to enter the neuron, making the inside more positive.
Hyperpolarisation
Some K+ channels remain open, causing the membrane potential to become more negative than resting state before stabilising
Repolarisation
Na+ channels inactivate, and K+ channels open, allowing K+ to exit the neuron, restoring the negative charge inside
How does an action potential travel down an axon?
The depolarization at one segment of the axon triggers the opening of Na+ channels in the next segment, propagating the action potential.
How does the CNS differentiate between weak and strong stimuli?
By the frequency of action potentials; higher frequency means a stronger stimulus.
What are the two types of refractory periods?
Absolute refractory period
Relative refractory period
Absolute refractory period
No new action potential can be generated.
Relative refractory period
A stronger stimulus is required to generate another action potential.
Why does the absolute refractory period occur?
Na+ channels are open and cannot be reactivated until they reset, ensuring unidirectional action potential propagation.
What occurs during the relative refractory period?
Most Na+ channels have reset, but some K+ channels remain open; a strong stimulus can trigger another action potential.
How does myelination affect action potential propagation?
Myelinated axons allow action potentials to “jump” between Nodes of Ranvier, speeding up conduction.
What happens to action potential frequency when stimulus strength increases?
Stronger stimuli generate more frequent action potentials, but the amplitude remains the same.
What is a synapse?
A junction where information is transferred from one neuron to another or to an effector cell.
What is the difference between presynaptic and postsynaptic neurons?
Presynaptic neuron sends the signal (conducts impulses toward the synapse).
Postsynaptic neuron receives the signal (transmits electrical signals away from the synapse).
What are the different types of synaptic connections?
Axodendritic - Between an axon and a dendrite.
Axosomatic - Between an axon and a cell body.
Axoaxonal - Between two axons.
What is the difference between chemical and electrical synapses?
Chemical synapses use neurotransmitters for communication.
Electrical synapses use direct ion flow through gap junctions for fast transmission.
What are the main parts of a chemical synapse?
Axon terminal of the presynaptic neuron, containing synaptic vesicles filled with neurotransmitters.
Receptor region on the postsynaptic neuron.
Synaptic cleft, a fluid-filled gap between the two neurons.
How is information transmitted across a synaptic cleft?
The presynaptic neuron releases neurotransmitters.
Neurotransmitters diffuse across the cleft and bind to receptors on the postsynaptic neuron.
This binding triggers an electrical signal in the postsynaptic neuron.
Why does synaptic transmission only occur in one direction?
Because neurotransmitters are only released from the presynaptic neuron and the postsynaptic neuron has the receptors.
What are the key steps in synaptic transmission?
An action potential arrives at the axon terminal.
Voltage-gated Ca²⁺ channels open, and Ca²⁺ enters the axon terminal.
Ca²⁺ entry triggers synaptic vesicles to release neurotransmitters via exocytosis.
Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane.
Binding of neurotransmitters opens ion channels, generating a graded potential.
Neurotransmitter effects are terminated by reuptake, enzymatic degradation, or diffusion away from the synapse.
Why is Ca²⁺ important in synaptic transmission?
Calcium triggers the release of neurotransmitters from synaptic vesicles into the synaptic cleft.
How are neurotransmitters removed from the synapse?
Reuptake – Neurotransmitters are taken back into the presynaptic neuron.
Enzymatic degradation – Enzymes break down neurotransmitters (e.g., acetylcholinesterase for acetylcholine).
Diffusion – Neurotransmitters drift away from the synapse.
What happens when a neurotransmitter binds to its receptor?
It opens ion channels on the postsynaptic neuron, leading to a graded potential that may trigger an action potential.
What is the difference between excitatory and inhibitory synapses?
Excitatory (EPSP): Neurotransmitters cause depolarization, increasing the likelihood of an action potential.
Inhibitory (IPSP): Neurotransmitters cause hyperpolarization, reducing the chance of an action potential.
How does an EPSP occur?
Neurotransmitter binding opens chemically gated ion channels, allowing Na⁺ and K⁺ to pass simultaneously.
How does an IPSP occur?
Neurotransmitter binding opens chemically gated ion channels permeable to K⁺ or Cl⁻, making the inside of the neuron more negative.
How do EPSPs and IPSPs influence a neuron?
A single EPSP cannot induce an action potential, but multiple EPSPs can summate to reach threshold.
IPSPs can also summate, making it harder for an action potential to occur.
What are the two types of summation?
Temporal summation
Spatial summation
Temporal summation
One or more presynaptic neurons transmit impulses in rapid succession to add up EPSPs.
Spatial summation
Multiple presynaptic neurons stimulate the postsynaptic neuron simultaneously to add up EPSPs.
How do temporal and spatial summation differ?
Temporal summation occurs when one neuron sends multiple signals quickly.
Spatial summation occurs when multiple neurons send signals at the same time.
What happens when EPSPs and IPSPs occur together?
They cancel each other out, preventing the neuron from reaching threshold.
What are the key differences between graded potentials and action potentials?
Graded potentials occur in the cell body and dendrites, travel short distances, and vary in strength.
Action potentials start at the axon hillock, travel long distances, and are all-or-nothing.
