Topic 9: Nervous System Flashcards
A. Sensitivity
Stimulus
any change in the environment that causes the organism to respond, and are detected by receptors.
A. Sensitivity
Receptors
- Receptors that can detect external stimuli include: eyes, ears, temperature receptors in the skin.
- Receptors that detect internal stimuli include: islets of Langerhans, osmoreceptors.
B. Organisation of the Nervous System
Two Parts of the Nervous System
Nervuos system is divided into two main parts:
* Central nervous system (CNS), consisting of the brain and spinal cord.
- Peripheral nervous system (PNS), consisting the cranial nerves, spinal nerves and the sense organs.
B. Organisation of the Nervous System
Stimulus Detection and Response Pathway
Nervous system serves to coordinate and regulate bodily activities.
- Receptors in sense organs detect stimuli and generate nerve impulses.
- These nerve impulses are transmitted by the nerve to the CNS.
- The CNS receive information from the receptors, integrate and interpret the information. A response is then initiated.
- Nerve impulses are then trasmitted by the nerves to the appropriate effectors for the response to be carried out.
- Effectors are either muscles or glands.
C. Nerves and Neurones
Neurones
- The nervous system is made up of nervous tissue, consists of nerve cells called neurones.
- Neurones are specialised cells adapted for the transmission of nerve impulses.
- Size and shape of the neurones differ in different parts of the nervous system but they have the same basic structure. Each neurone consists of a cell body and a number of nerve fibres. Nerve fibres are cytoplasmic extensions from the cell body. These nerve fibres are termed axons or dendrons depending on the direction of nerve transmission from the cell body.
C. Nerves and Neurones
Types of Neurones
- Sensory neurones transmit nerve impulses from the receptors to the CNS.
- Motor neurones transmit nerve impulses from the CNS to the effectors.
- Relay neurones transmit nerve impulses from sensory neurone to motor neurone inside the central nervous system.
C. Nerves and Neurones
Motor End Plate
Motor end plate is formed when the end branch of an axon comes into contact with the muscle fibre. Nerve impulses are transmitted across the moto end plate by chemicals which simulate the muscle.
D. Neurone Pathways
Pathway of the Sensory Neurone
Transmit nerve impulses from: sense organs / receptors
to: central nervous system
Location: in between sense orgagns and CNS
D. Neurone Pathways
Pathway of the Relay Neurone
Transmit nerve impulses from: sensory neurones
to: motor neurones
Location: in the CNS
D. Neurone Pathways
Pathway of the Motor Neurone
Transmit nerve impulses from: central nervous system
to: effectors (muscle or gland)
Location: in between CNS and effectors
E. Structure of a Neurone
Structure of a Neurone
- a cell body containing a nucleus and a number of fine cytoplasmic processes (nerve fibres)
- nerve fibres: dendrons transmit impulses toward the cell body, and axons transmits impulses away from the cell body
- myelin sheath consists of Schwann cells that wrap around the axon
- in between two Schwann cells is the node of Ranvier
E. Structure of a Neurone
Cell Body
Contains a nucleus and many organelles (e.g. ER, GA, mitochondria, ribosomes).
E. Structure of a Neurone
Nerve Fibres
- Cytoplasmic extensions from the cell body
- Comprised of dendrons and axons
E. Structure of a Neurone
Dendrons
- Transmit impulses towards cell body.
- Receive impulses from other neurones or receptors
- Usually branch into many smaller, numerous extensions called dendrites
E. Structure of a Neurone
Axons
- Transmits impulses away from the cell body to other neurones or to muscles/ glands.
- Axons are usually long (up to a metre in large animals).
E. Structure of a Neurone
Schwann Cell
- In vertebrates, Schwann cells wrap around the axons and dendrons of many neurones at regular intervals.
- The membranes of Schwann cells (neurilemma) form the myelin sheath (composed mainly of lipid myelin). The myelin sheath is located outside the plasma membrane of the axon.
- Neurones which are enclosed by Schwann cells are called myelinated neurones.
E. Structure of a Neurone
Functions of Myelin Sheath
- Protection and insulation.
- Presence of myelin sheath prevents the loss of current (in the form of Na+ and K+) from the axon.
- This increases the speed of transmission of nerve impulses along the axon.
- Therefore myelinated neurones transmit impulses faster than non-myelinated neurons.
E. Structure of a Neurone
Nodes of Ranvier
- Gaps (about 1mm) between Schwann cells, where myelin sheath is absent
- Allows nerve impulses to jump from node to node
E. Structure of a Neurone
Synaptic Knobs
- These are bulbous structures found at the ends of axons.
- They relay nerve impulse from one neurone to another through the release of chemicals called neurotransmitters, which are contained in vesicles known as synaptic vesicles.
E. Structure of a Neurone
Un/Non-Myelinated Neurons
- Some neurons do not need to transfer non-vital nerve impulses quickly, hence do not need to be myelinated
- If all neurons were myelinated, too much space would be taken up by the neurons.
F. Transmission of Nerve Impulse
Transmission of Nerve Impulses
- When a stimulus is received by the sensory neurone, this information is transmitted to the control centre, which then initiates an apppropriate response via motor neurones.
- Stimulus is detected by the receptor (different kinds of sensory neurones)
- Sensory neurones passes on information in the form of nerve impulse to the CNS (control centre), where relay neurones in the brain or spinal cord receives the impulses.
- These relay neurones then passes on information in the form of nerve impulse to the effector (muscle or gland) through the motor neurones.
- The triggered effector creates a response to the stimuli.
G. Brain & Spinal Cord
Nerves
- A nerve is a bundle of hundreds of nerve fibres (strands of cytoplasm extending from the cell body) bundled together and covered by connective tissue.
- Nerves may emerge from the brain (cranial nerve) or the spinal cord (spinal nerve). They may contain, a) sensory nerve fibres only; b) motor nerves fibre only; c) both sensory and motor nerve
G. Brain & Spinal Cord
Grey Matter
- Consists mainly of the cell bodies of the neurones
- It forms the outer layers of the brain and the central parts of the spinal cord
G. Brain & Spinal Cord
White Matter
- Consists mainly of nerve fibres
- It forms the central parts of the brain and the outer layers of the spinal cord
G. Brain & Spinal Cord
Dorsal Root Ganglia
Each segment of the spinal cord is associateed with a pair of ganglia, called dorsal root ganglia, which are situated just outside of the spinal cord. These ganglia contain cell bodies of sensory neurones. Axons of these sensory neurones travel into the spinal cord via the dorsal roots.
G. Brain & Spinal Cord
Ventral Roots
Ventral roots consist of axons from motor neurones, which bring information to the periphery from cell bodies within the CNS.
G. Brain & Spinal Cord
Spinal Nerves
Dorsal roots and ventral roots come together and becme spinal nerves.
H. Voluntary Action
Definition of a Voluntary Action
An action under the control of a will.
H. Voluntary Action
Process of a Voluntary Action
- Eyes see the object.
- A nerve impulse is sent to
the brain. - The brain calculates the position
of the peanut and predicts how you
should move the chopsticks. - The brain then sends an impulse
along the relay neurone in your spinal
cord to the appropriate motor
neurones. - This nervous impulse is sent to the
effector i.e. the appropriate muscles
in your arm. - Muscles contract and the object is picked up.
I. Reflex Action
Definition of a Reflex Action
An immediate response to a specific stimulus without conscious control.
I. Reflex Action
Classifications of Reflex Actions
Spinal reflexes are controlled by the spinal cord, for example withdrawal of hand from a hot pan, knee-jerk reflex
Cranial reflexes are controlled by the brain (but not the conscious will) and usually occur in the head region, for example, pupil reflex, blinking and salivation.
I. Reflex Action
Reflex Arc
A reflex arc is the shortest pathway by which nerve impulses travel from the receptor to the effector in a reflex action.
Components:
* Receptor or sense organ
* Sensory neurone
* Relay neurone in the CNS (brain or spinal cord)
* Motor neurone
* Effector (muscle or gland)
I. Reflex Action
Withdrawal of Hand from a Hot Pan
- Heat from the pan stimulates temperature receptors in the skin.
- Nerve impulses are generated by the receptor, which are transmitted along the sensory neurone to the spinal cord.
- In the spinal cord, the impulses are transmitted across a synapse to the relay neurone and then across another synapse to the motor neurone.
- The nerve impulses are transmitted across the synapses by the release of neurotransmitters.
- Nerve impulses leave the spinal cord along the motor neurone to the bicep muscles (effector).
- The bicep muscles contract, to bring out the sudden and immediate withdrawal of the hand.
- When the nerve impulses from the receptors arrive at the spinal cord, the relay neurone also transmits the nerve impulses to the brain (not part of the reflex arc). This makes the brain aware of what is happening.
J. Comparison between Reflex and Voluntary Action
Comparison between Reflex and Voluntary Action
Does not involve conscious control vs involves conscious control
Stimulus is always involved vs stimulus may not always be involved
Occurs faster vs occurs slower
The same stimulus will always result in the same response vs the same stimulus may not always result in the same response
K. Comparison between Nervous and Endocrine System
Comparison between Nervous and Endocrine System
Involves nerve impulses (electrical signals) and chemical (neurotransmitters) vs involves hormones (chemical substances)
Impulses are transmitted by neurones.
Hormones are transmitted by blood
Usually quick responses vs usually slower responses
Responses are short-lived vs responses may be short or long-lived
May be voluntary or involuntary vs always involuntary
Usually localised vs tend to affect one or more target organs
