3.8 -the Nervous System Flashcards
What does the nervous system do (broad 3 points)
1) detects changes or stimuli inside the body and in the environment
2) processes and stores information
3) initiates a response
What is a stimulus?
A detectable change in the internal or external environment of an organism that produces a response in that organism
What give an organism its senses?
Sensory receptors
What are sensory receptors?
Transducers because they detect energy in one form and convert it into a electrical energy.
What are electrical impulses also known as?
Where do they travel?
What do they do?
Called: nervous impulses
Travel: travel along neurones
Action: initiate a response in an effective which may be a muscle or gland
If visible light is the stimulus what is the sensory receptor location? And sense?
Sensory receptor= Retina
Sense= sight
If sound is the stimulus what is the sensory receptor location and sense?
Sensory receptor= inner ear
Sense= sound
If pressure is the stimulus what is the sensory receptor location and what is the sense
Sensory receptor location= dermis of the skin
Sense= touch
If temperature is the stimulus what is the sensory receptor location and sense?
Sensory receptor location= dermis of the skin
Sense= temperature
If gravity is the stimulus where is the sensory receptor location and sense?
Sensory receptor location = middle ear
Sense= balance
List where mammals may sense pressure?
Dermis of the skin, blood vessels, UV light, electric fields, changes in humidity, magnetic fields, tissue damage and osmolarity of fluids
What is a nerve?
A bundle of neurones or nerve fibres
What are the 2 main parts of the central nervous system
1) central nervous system (CNS)
2) peripheral nervous system (PNS)
What does the CNS comprise of?
Comprises of the brain and the spinal cord
What is the role of the nervous system?
The CNS processes information provided by a stimulus.
What are the parts of the CNS surrounded by?
Surrounded by a tough protective membrane collectively called meninges
Describe the structure of the spinal cord
- white matter contains nerve fibres surrounded by myelin which is fatty so looks white
- the grey matter has much less myelinated and is largely the nerve fibres of relay neurones and the cell bodies of relay and motor neurones.
What is the peripheral nervous system (PNS) comprised of?
The somatic nervous system and the autonomic nervous system
Describe the somatic nervous system
- Pairs of nerves that originate in the brain or spinal cord and their branches.
- nerves contain the fibres of sensory neurones which carry impulses from receptors to the CNS, and motor neurones which carry impulses away from the CNS to effectors
Describe the autonomic nervous system
Provides unconscious control of the function of internal organs e.g heartbeat and digestion.
How can the speed at which we detect a change in stimuli benefit an organism
The ability to detect and respond to stimuli increases an organisms chance of survival
What is the name of the simplest type of nervous response to a stimulus?
A reflex arc
What is a reflex arc?
Give an example of a common reflex arc.
The neural pathway taken by the nervous impulses of a reflex action.
Example: the withdrawal of a reflex e.g when you immediately withdraw your hand when placed on a hot object.
What is a reflex action?
A rapid, automatic, involuntary response resulting from nervous impulse initiated by a stimulus. (Generally has a protective function.)
Give the elements of a reflex arc in order
- Stimulus (e.g heat)
- Receptor (temperature and pain receptors in the dermis of the skin)
- Sensory neurone (sends impulse up the arm to the spinal cord)
- CNS (relay neurone in spinal cord transmits an impulse from a sensory neurone to a motor neurone)
- Motor neurone (sends impulse to an effective in this case a muscle)
- Response (arm muscles contract and the hand is removed from heat source)
What are some reflex arcs missing, give an example
Reflex arcs of some reflex actions do not have a relay neurone e.g the knee jerk reflex. The sensory neurone synapses directly with the motor neurone
What is a nerve net?
The simplest type of nervous system, a diffuse network of cells that group into ganglia, but do not form a Brain.
What are the two types of cells in a nerve net?
- ganglion cells which provide connections in several directions
- sensory cells which detect stimuli e.g light sound touch or temperature
What is the model organism for studying nerve nets?
Why?
Model organism: Hydra, in the phylum Cnidaria
Model organism because:
1)has a simple pattern
2)is easy to manipulate in experiments
3)regenerates rapidly e.g when replacing a lost tentacle
Where is a hydras nerve net located?
In its ectoderm, the outer of the two layers of cells of its body wall.
How does the nerve net benefit the hydra?
It allows the hydra to sense light, physical contact and chemicals, so in response it can contract, perform locomotion, hunt and feed. (Even without a brain it shows complex movements and behaviour).
One negative of the hydra nerve net
It can’t detect the direction of a stimulus, although a larger stimulus stimulates more cells and triggers a larger response.
Compare and contrast the nervous system in the Hydra and humans
Nervous system type: Hydra= nerve net, Humans= CNS
Number of cell types in nervous system: Hydra= 2, Human= many
Regeneration: Hydra= rapid, Human= very slow If at all
Myelin sheath: Hydra =absent, Human =present
Conduction speed: Hydra =slow (5 ms-1), Human =fast (up to 120ms-1)
Ability to regenerate neurones: Hydra =Present, Human =Absent
What is important to note about certain hormones?
Vertebrate hormones e.g steroids occur in the hydras nerve net. However, the nervous systems of hydra and vertebrates are so different that it is unlikely that the hormones have the same function
What are nerve cells/neurones?
Specialised cells adapted to rapidly carry nervous impulses from one part of the body to another
What are the three types of neurones?
- Sensory neurone (carries impulses from the sense receptors or organs to the CNS)
- Motor neurone (carries impulses from the CNS to the effector organs I.e muscles or glands)
- Relay neurone (receives impulses from sensory neurone or other relay neurones and transmits then to motor neurones on other relay neurones
List the parts of the mammalian motor neurone
Cell body/centron Cytoplasm Nucleus Nissl granules Dendrite Axon Schwann cells Myelin sheath Nodes of ranvier Synaptic end bulb Axon ending/terminal
What is the function of the mammalian motor neurones cell body/centron
Contains a nucleus and granular cytoplasm
What is the function of the mammalian motor neurones cytoplasm
Granular; contains many ribosomes
What is the function of the mammalian motor neurones nucleus
Holds DNA
What is the function of the mammalian motor neurones Nissl granules
Cytoplasmic granules comprising ribosomes grouped in RER
What is the function of the mammalian motor neurones Dendrite
Thin fibre carrying impulses towards cell body, a cell body may have several dendrites
What is the function of the mammalian motor neurones axon
Thin fibre carrying impulses away Fromm cell body, a cell body has only one axon
What is the function of the mammalian motor neurones Schwann cells
-surround and support nerve fibres, in vertebrate embryos they wrap around the developing axons many times and withdraw their cytoplasm, leaving a multi-layered phospholipid myelin sheath