topic 8 Flashcards
What are the two main divisions of the nervous system?
Central Nervous System (CNS) - Brain and spinal cord.
Peripheral Nervous System (PNS) - Sensory and motor nerves.
What is the function of sensory and motor nerves in the Peripheral Nervous System?
Sensory nerves: Carry sensory information from receptors to the CNS.
Motor nerves: Carry motor commands from the CNS to effectors.
What are the two subdivisions of the Peripheral Nervous System?
Autonomic Nervous System (involuntary): Stimulates smooth muscles, cardiac muscles, and glands.
Somatic Nervous System (voluntary): Stimulates skeletal muscles.
What are the roles of the Sympathetic and Parasympathetic Nervous Systems?
Sympathetic: Prepares the body for “fight or flight” responses.
Parasympathetic: Prepares the body for “rest and digest.”
What is the difference between a neuron and a nerve?
Neuron: A single cell.
Nerve: A more complex structure containing a bundle of axons from many neurons, surrounded by a protective coating.
What are the basic characteristics of a neuron?
Cell body: Contains the nucleus and organelles within the cytoplasm.
Dendrites: Conduct impulses toward the cell body.
Axon: Transmits impulses away from the cell body.
What is the function of the cell body in a neuron?
The cell body contains most organelles, including the nucleus and RER, to make proteins and neurotransmitters.
What is the role of dendrites in a neuron?
Dendrites are extensions of the cell body that carry nerve impulses towards the cell body.
What is the function of the axon in a neuron?
The axon is a long fiber that carries impulses away from the cell body.
What is the myelin sheath and its function?
The myelin sheath covers the axon and is made up of membranes of Schwann cells. It insulates the axon and speeds up nerve impulses.
What are Nodes of Ranvier and their function?
Nodes of Ranvier are gaps between Schwann cells that help in the rapid transmission of nerve impulses.
What are Schwann cells, and what do they do?
Schwann cells surround and insulate the axon and remove cell debris by phagocytosis.
What are the three different types of neurons?
Motor neurons: Transmit impulses away from the CNS to an effector (muscle/gland). They have long axons and short dendrites.
Sensory neurons: Carry impulses from sensory cells to the CNS.
Relay (intermediate) neurons: Mostly found in the CNS, transmit impulses from sensory to motor neurons, and have numerous short processes.
What is the myelin sheath, and what is it made of?
The myelin sheath is a fatty insulating layer around the axon, made up of Schwann cells wrapped around the axon. It affects how quickly nerve impulses pass along the axon.
What are nerve impulses, and what are they also called?
Nerve impulses are electrochemical changes, also known as action potentials.
What does each neuron consist of?
Cell body: Contains the nucleus and large amounts of rough endoplasmic reticulum for protein and neurotransmitter production.
Axon: A single long fiber that transmits signals.
Dendrites: Smaller branched fibers that carry impulses toward the cell body.
What is the role of Schwann cells?
Schwann cells surround the axon to protect and insulate it. Their membranes are rich in a lipid called myelin.
What are the three main types of neurons and their roles?
Motor neurons: Carry impulses to effectors like muscles and glands.
Sensory neurons: Carry impulses from receptors to the CNS.
Intermediate (relay) neurons: Link sensory and motor neurons.
What is a reflex arc?
A reflex arc is a simple nerve pathway responsible for reflexes, which are rapid and involuntary responses to stimuli.
What does the knee-jerk reflex involve?
It involves two neurons: a sensory neuron communicating directly with a motor neuron to connect receptor cells with effector cells.
What is the first step in the reflex pathway?
Receptors detect a stimulus and generate a nerve impulse.
What happens after a receptor generates a nerve impulse?
Sensory neurons conduct the nerve impulse to the CNS along a sensory pathway.
How does a sensory neuron enter the spinal cord?
Sensory neurons enter the spinal cord through the dorsal route.
What happens when the sensory neuron reaches the spinal cord?
The sensory neuron forms a synapse with a relay neuron in the spinal cord.
What is the role of the relay neuron in the reflex pathway?
The relay neuron forms a synapse with a motor neuron, which leaves the spinal cord through the ventral route.
What happens after the motor neuron is activated?
The motor neuron carries impulses to an effector, such as a muscle, which produces a response (e.g., contracting the biceps to move the arm away from a stimulus).
What do most nerve pathways involve?
Most nerve pathways involve numerous neurons within the CNS, where sensory neurons connect to a range of neurons to pass impulses to the brain for a coordinated response.
What is an example of a reflex action shown in the diagram?
The biceps contract to raise the arm away from a flame as part of the reflex response.
What is the pupil reflex?
The pupil reflex is an automatic response that adjusts the size of the pupil to changes in light intensity, ensuring the right amount of light enters the eye to protect the retina and optimize vision.
How does the pupil respond to bright light?
The pupil constricts to reduce the amount of light entering the eye.
How does the pupil respond to dim light?
The pupil dilates to let in more light.
What controls the size of the pupil?
The iris controls the size of the pupil by using a pair of antagonistic muscles:
Radial muscles: Controlled by the sympathetic nervous system; they contract to dilate the pupil in dim light.
Circular muscles: Controlled by the parasympathetic nervous system; they contract to constrict the pupil in bright light.
What happens to the pupil in bright light?
Circular muscles contract, reducing the pupil size.
Radial muscles relax.
What happens to the pupil in dim light?
Circular muscles relax, increasing the pupil size.
Radial muscles contract.
How does light intensity affect the pupil reflex?
High light levels stimulate photoreceptors in the retina.
This causes nerve impulses via the optic nerve to the CNS, specifically coordinating neurons in the midbrain, which aim to reduce the amount of light entering the eye to protect the retina.
What is the role of sensory neurons in the reflex pathway for pupil constriction?
Sensory neurons carry impulses from the photoreceptors in the retina to relay neurons in the midbrain.
What do relay neurons do in the reflex pathway for pupil constriction?
Relay neurons pass impulses to parasympathetic motor neurons.
What is the function of parasympathetic motor neurons in the pupil reflex?
Parasympathetic motor neurons send signals to the circular muscles of the iris, causing them to contract, which leads to pupil constriction. They also cause radial muscles to relax.
What is the definition of resting potential?
Resting potential is the potential difference across the membrane of a neuron when it is not transmitting an action potential. It is typically around -70 mV in neurons.
Why is the inside of the axon more negative relative to the outside during resting potential?
This is due to the action of the sodium-potassium pump and the selective permeability of the membrane to potassium ions.
How does the sodium-potassium pump maintain resting potential?
The pump actively transports 3 Na⁺ ions out of the neuron and 2 K⁺ ions into the neuron, creating a net negative charge inside the axon.
Why is the resting potential essential?
It maintains the readiness of the neuron to generate and propagate an action potential.
Why does resting potential occur?
It happens because of the uneven distribution of ions inside and outside the axon:
Inside the axon: More potassium ions (K⁺) and negatively charged molecules (organic anions).
Outside the axon: More sodium ions (Na⁺) and chloride ions (Cl⁻).
What creates the resting potential?
The difference in charge across the membrane due to ion distribution creates the resting potential, which is around -70 mV.
Why is it called “resting” potential?
Because the neuron is not actively sending a signal.
What are the two main factors maintaining the resting potential?
Sodium-potassium pump.
Electrical gradient due to K⁺ diffusion.
How does the sodium-potassium pump function?
It uses ATP to pump 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell against their concentration gradients.
How does potassium ion diffusion contribute to resting potential?
Potassium ions diffuse out of the cell due to the concentration gradient, creating a negative charge inside the cell. This negative charge eventually attracts potassium ions back into the cell until equilibrium is reached, maintaining the resting potential at -70 mV.
What is the steady state of the resting potential?
There is no net movement of K⁺ ions, and the potential difference across the membrane is maintained at -70 mV.
What is the difference between a neurone and a nerve?
A neurone is a single cell that transmits electrical impulses, while a nerve is a bundle of axons from many neurones surrounded by a protective covering.
What are the two types of thin extensions from a neurone’s cell body?
Dendrites – conduct impulses towards the cell body.
Axon – transmits impulses away from the cell body.
What are the three main types of neurones and their functions?
Motor Neurones – Carry impulses from the CNS to effectors (muscles or glands).
Sensory Neurones – Carry impulses from receptors to the CNS.
Relay Neurones – Connect sensory and motor neurones within the CNS.
What is the myelin sheath and its function?
The myelin sheath is a fatty insulating layer that surrounds the axon, produced by Schwann cells. It speeds up impulse transmission by allowing saltatory conduction.
What is a reflex arc?
A reflex arc is a rapid, automatic response to a stimulus that does not involve conscious thought.
What are the five steps in a reflex arc?
Receptor detects a stimulus (e.g., pain).
Sensory neurone carries impulse to the spinal cord.
Relay neurone in the spinal cord processes the signal.
Motor neurone carries impulse to the effector.
Effector (muscle or gland) produces a response.
How does the pupil respond to bright light?
The pupil constricts (gets smaller) to limit light entry. Circular muscles contract, radial muscles relax.
How does the pupil respond to dim light?
The pupil dilates (gets larger) to allow more light in. Radial muscles contract, circular muscles relax.
What part of the brain controls the pupil reflex?
The midbrain coordinates the pupil reflex.
What is an action potential?
An action potential is a large change in voltage across the membrane of a neurone, allowing impulses to be transmitted.
What are the three main stages of an action potential?
Depolarisation – Sodium (Na⁺) channels open, Na⁺ enters, making the inside more positive.
Repolarisation – Sodium channels close, potassium (K⁺) channels open, K⁺ leaves, restoring negativity.
Restoring Resting Potential – Sodium-potassium pump restores ion balance.
What is the ‘all-or-nothing’ principle?
Action potentials only occur if the threshold potential is reached. The size of the stimulus does not affect the action potential size, only the frequency.
How is an impulse passed along an axon?
The action potential at one section of the axon triggers the next section to depolarise, like a domino effect.
What is the refractory period?
A short period (~5ms) after an action potential where another impulse cannot be generated, ensuring one-way transmission.
What factors affect the speed of impulse conduction?
Axon diameter – Wider axons conduct faster.
Myelination – Myelinated axons conduct faster due to saltatory conduction (impulse jumps between Nodes of Ranvier).
What is saltatory conduction?
In myelinated neurones, the impulse jumps between Nodes of Ranvier, making conduction much faster.
How does multiple sclerosis (MS) affect nerve conduction?
MS damages the myelin sheath, slowing down or blocking nerve impulses, leading to weaker muscle responses and loss of coordination.
What is a synapse?
A synapse is the small gap between two neurones where neurotransmitters chemically transmit nerve impulses.
What are the three stages of synaptic transmission?
Neurotransmitter release – Action potential triggers Ca²⁺ entry, causing vesicles to release neurotransmitter into the synaptic cleft.
Stimulation of the postsynaptic membrane – Neurotransmitter binds to receptors, opening Na⁺ channels to trigger depolarisation.
Inactivation of the neurotransmitter – It is broken down (e.g., acetylcholinesterase breaks down acetylcholine) or reabsorbed into the presynaptic neurone.
What is an excitatory synapse?
An excitatory synapse increases the likelihood of an action potential by making the postsynaptic membrane more permeable to Na⁺.
What is summation, and what are its types?
Spatial summation – Multiple presynaptic neurones release neurotransmitters onto a single postsynaptic neurone.
Temporal summation – A single neurone fires rapidly, building up enough neurotransmitter to trigger an action potential.
What is an inhibitory synapse?
An inhibitory synapse reduces the likelihood of an action potential by opening Cl⁻ and K⁺ channels, causing hyperpolarisation.
How do excitatory and inhibitory synapses affect nerve transmission?
Excitatory synapses increase depolarisation, making action potentials more likely.
Inhibitory synapses cause hyperpolarisation, making action potentials less likely.
Why is the balance of excitatory and inhibitory synapses important?
It determines whether a neurone fires. This balance controls nerve responses, preventing overstimulation or insufficient activation.
How is the resting potential maintained in a neurone?
The resting potential is maintained by the sodium-potassium pump, which actively transports 3 Na⁺ ions out and 2 K⁺ ions into the neurone, creating a negative charge inside. Additionally, the membrane is more permeable to K⁺, allowing K⁺ to diffuse out, contributing to the negative resting potential.
What is the sequence of events during the generation of an action potential?
- Depolarisation: Stimulus causes Na⁺ channels to open; Na⁺ enters the neurone, making the inside positive.
- Repolarisation: Na⁺ channels close; K⁺ channels open; K⁺ exits, restoring negativity inside.
- Hyperpolarisation: Excessive K⁺ outflow makes the inside more negative than resting potential.
- Restoration: Sodium-potassium pump restores resting potential by moving Na⁺ out and K⁺ in.
What is the process of synaptic transmission at a chemical synapse?
- Action potential arrives at presynaptic terminal.
- Voltage-gated Ca²⁺ channels open; Ca²⁺ enters.
- Synaptic vesicles fuse with presynaptic membrane; neurotransmitter (e.g., acetylcholine) is released into synaptic cleft.
- Neurotransmitter binds to receptors on postsynaptic membrane.
- Ion channels open; Na⁺ enters postsynaptic neurone, causing depolarisation.
- If threshold is reached, action potential is generated in postsynaptic neurone.
- Neurotransmitter is degraded by enzymes (e.g., acetylcholinesterase) or reabsorbed, terminating the signal.
What are the components of a reflex arc and their functions?
- Receptor: Detects stimulus.
- Sensory Neurone: Transmits impulse to CNS.
- Relay Neurone: Processes impulse within CNS.
- Motor Neurone: Carries impulse from CNS to effector.
- Effector: Muscle or gland that produces response.
What happens during the pupil reflex in response to bright light?
Bright light stimulates photoreceptors; impulses travel via sensory neurones to the brain; motor neurones activate circular muscles of the iris to contract, causing pupil constriction, reducing light entry.
How does myelination affect nerve impulse conduction velocity?
Myelination increases conduction velocity by enabling saltatory conduction, where action potentials jump between nodes of Ranvier, speeding up transmission.
What is the difference between excitatory and inhibitory synapses?
Excitatory synapses increase the likelihood of action potentials by causing depolarisation (e.g., Na⁺ influx). Inhibitory synapses decrease this likelihood by causing hyperpolarisation (e.g., Cl⁻ influx or K⁺ efflux).
What are the two types of summation in neural transmission?
- Spatial Summation: Multiple presynaptic neurones release neurotransmitters simultaneously onto one postsynaptic neurone.
- Temporal Summation: One presynaptic neurone releases neurotransmitters repeatedly in quick succession.
Why is the refractory period important in nerve impulse transmission?
It ensures unidirectional impulse propagation and limits the frequency of action potentials, preventing overstimulation.
