What are the four main parts of the brain and outline their main roles?
- The cerebrum (largest part, organises higher thought processes).
- The cerebellum (coordinates movement and balance).
- The hypothalamus and pituitary complex (organises homeostatic responses and controls physiological responses).
- The medulla oblongata (coordinates many of the autonomic responses).
What is the structure of the cerebrum?
- The cerebrum has two cerebral hemispheres, which are connected via a bundle of nerve fibres called the corpus callosum.
- The outermost layer of the cerebrum consists of a thin layer of nerve cell bodies called the cerebral cortex.
What do the ‘higher brain’ functions include?
- conscious thought
- conscious actions (including the ability to override some reflexes)
- emotional responses
- intelligence, reasoning, judgement & decision making
- factual memory
What is the sensory area of the cerebral cortex responsible for?
-Sensory areas receive action potentials indirectly from the sensory receptors.
What do the association areas in the cerebral cortex do?
-They compare sensory inputs with previous experience, interpret what the input means and judge an appropriate response.
What do the motor areas of the cerebral cortex do?
-Motor areas send action potentials to various effectors (muscles and glands).
How do the sizes of the regions in the sensory areas of the cerebral cortex vary?
-The sizes of the regions allocated to receive input from different receptors are related to the sensitivity of the area that inputs are received from
How do the sizes of the regions in the motor areas of the cerebral cortex vary?
-The sizes of the regions allocated to deal with different effectors are related to the complexity of the movements needed in parts of the body.
The cerebellum is involved with balance and fine coordination of movement. To do this, what must it do?
-It must receive information from many sensory receptors and process information accurately.
What do the sensory receptors that supply information to the cerebellum include?
- The retina
- The balance organs in the inner ear
- The spindle fibres in the muscles which give information about muscle length and joints.
Where is the conscious decision to contract voluntary muscles initiated?
- In the cerebral cortex
- However, the cerebral cortex does not supply the complex signals required to coordinate complex movements.
The cerebellum coordinates the fine control of muscular movements such as:
- Maintaining body position and balance e.g. riding a bike.
- Judging the position of objects and limbs while moving and playing a sport.
- Tensioning muscles in order to use tools and play musical instruments effectively.
- Coordinating contraction and relaxation of antagonistic skeletal muscles when walking and running.
How does complex activity become ‘programmed’ into the cerebellum?
- Fine control of muscular movements often requires learning.
- Once learnt, such activities may become second nature and involve much unconscious thought.
- This coordination requires complex nervous pathways that are strengthened in practice.
How does the cerebellum control coordination (in terms of neurones and action potentials)?
-Neurones from the cerebellum conduct action potentials to the motor areas so that the motor output to the effectors can be finely controlled.
How are the cerebrum and cerebellum connected?
By the pons.
What does the hypothalamus control?
Homeostatic mechanisms in the body.
-It contains its own sensory receptors and acts by negative feedback to maintain a constant internal environment.
How does the hypothalamus control temperature?
- Detects changes in core body temperature.
- Also receives sensory output from temperature receptors in skin.
- It will initiate responses to temperature change that regulate body temperature within a narrow range.
- Responses may be mediated by the nervous system or hormonal system (via the pituitary gland)
How is the hypothalamus involved in osmoregulation?
- Contains osmoreceptors that monitor the water potential in the blood.
- When the water potential changes, the osmoregulatory centre initiates responses that bring about a reversal of this change.
- The response is mediated by the hormonal system via the pituitary gland.
How does the hypothalamus work with the posterior lobe of the pituitary gland?
- Posterior lobe is linked to the hypothalamus by specialised neurosecretory cells.
- Hormones (e.g. ADH) that are manufactured in the hypothalamus, pass down the neurosecretory cells and are released into the blood from the pituitary gland.
What does the anterior lobe of the pituitary gland do?
-Produces its own hormones which are released into the blood in response to releasing factors produced by the hypothalamus.
What are releasing factors?
Hormones that need to be transported only a short distance from the hypothalamus to the pituitary.
What do the hormones from the anterior pituitary control?
A number of physiological processes in the body, including response to stress, growth, reproduction, and lactation.
What does the medulla oblongata control?
-The non-skeletal muscles (the cardiac muscles and involuntary smooth muscles).
How does the medulla oblongata control the non-skeletal muscles?
By sending action potentials through the autonomic nervous system.
The medulla oblongata contains centres for regulating several vital processes. What do these vital processes include?
- The cardiac centre, which regulates heart rate.
- The vasomotor centre, which regulates circulation and blood pressure.
- The respiratory centre, which controls rate and depth of breathing