The Brain (p&a r 5.1.5 g, h, i, j, k)
reflex actions
autonomic nervous system - sympathetic & parasympathetic nervous systems
organisation of nervous system
the hypothalamus & pituitary gland
brain function - Medulla Oblongata
brain function - Cerebellum
brain function - Cerebrum
fight or flight (ANS —> sympathetic)
The 2 cerebral hemispheres together are known as the cerebrum
Largest part of the brain
Receives sensory information
Interprets it & sends out motor signals to respond
Site of:
- Learning
- Reasoning
- Intelligence
- Personality
- Memory
Bullets from WWI provided huge amounts of data of what parts of the brain did what
bullets damaged different parts of the brain doctors & scientists had records of which function were lost
With so much data available they were able to deduce within areas of the brain controlled each function
Right hemisphere responsible for left side of body
Left hemisphere responsible for right side of body
Cerebral hemispheres are connected by the corpus callosum
3 main areas:
1) Primary sensory areas
These are the 1st regions to sensory info. Different areas deal with different senses
E.g. primary visual area deals with vision, primary auditory area deals with hearing
2) Association (secondary) areas
Receive info from 2 or more primary sensory areas & integrate the info.
Our cerebrum can now make sense of what our eyes, ears etc tell us bout the environment
Huge amount of cerebrum is made of association areas
The pre-frontal association area (pre-frontal cortex) is concerned with planning actions & movements:
Focussing attention
Predicting consequences of actions
Anticipating events in environment
Planning for future
Coordinating & adjusting complex behaviours
personality
There is another area called the Limbic association area which is concerned with emotions & memory
3) Motor areas
Send impulses to effectors (muscles & glands)
Decision to catch a ball is arrived out in Cerebrum
Actually carrying out the act is controlled & coordinated but the cerebellum
It’s therefore in charge of certain non-conscious, skeletal muscle operation e.g.
Standing upright without falling over
Driving a car without thinking
Writing
Drawing
Balance
When repeated sequence of actions becomes ‘second nature’ our cerebellum has taken over control & we no longer have to be conscious the whole time. Learning to ride a bike is a good example
At 1st your cerebrum is processing & integrating lots of info, eventually cerebellum takes over & you no longer are consciousness about what you’re doing.
Processes info from:
Retina
Balance organs of inner ear
Muscle spindles
Joints (proprioceptors)
Fish & birds have massive cerebellum proportionate to their size
Imagine a fish or bird remaining stationary in fast flowing river or high wind
Lots of info must be processed & immediate adjustments made
Control non-skeletal muscles
E.g. cardiac & involuntary smooth muscles
Sends action potentials out through the ANS (autonomic nervous system)
Regulates
Cardiac centre (heart rate)
Vasomotor centre (circulation & blood pressure)
Rate & depth of breathing
Positive feedback from sensory receptors coordinate vital function
hypothalamus & posterior pituitary gland
Hypothalamus controls homeostatic mechanisms of the body
Contains:
Temperature receptors
Osmoreceptors (intimate ADH release with Posterior Lobe of Pituitary gland)
Receives nervous input from the skin (early warning system)
Works together with Pituitary gland
Pituitary gland consists of 2 lobes
ADH is made in hypothalamus & passes down neurosecretory cells to posterior lobe of Pituitary gland to be released
Anterior pituitary gland
Produces own hormones
Released into blood when receives signals from hypothalamus
Signals arrive from the hypothalamus via the blood in from of releasing factors
Anterior lobe can then release a variety of hormones controlling
Stress
Growth
Reproduction
lactation, etc…
Broca's area
Wernicke's area
If this region of the cerebrum is damaged patient could understand langue but could not speak = turns speech into comprehensible sounds
Suggests it’s a motor area as can understand but not speak
When damaged patient could speak but their sentences sounded normal but were meaningless - did not make sense, could not repeat words or phrases but were unaware of speech problem = makes meaningful speech
Suggests association area that is messing things up due to damage
Damage to the the bundle of neurones connecting the 2 areas results in patient being able to understand language but unable to repeat words
Central nervous system (CNS)
Peripheral nervous system (PNS)
Comprises of brain & spinal chord
86 billion neurones
Most neurones are:
Relay neurones which allow complex connections
Most are non-myelinated
Grey in colour
Spinal Chord
Contains many non myelinated relay neurones making up the grey matter
Also contain myelinated neurones making up outer regions of white matter
Myelinated neurones can carry impulses up & down spinal chord at high speed over long distances
Peripheral nerves enter & leave spinal chord carrying action & potential to & away from body
Ensures rapid communication between sensory receptors, the CNS & effectors
Peripheral nerves:
composed of sensory & motor neurones
usually bundled together in connective tissue sheath to form nerves
Sensory nervous system
Motor nervous system
Somatic nervous system
Autonomic nervous system
Sensory fibres entering their CNS are dendron of the sensory neurone
are myelinated.
Their cell body is in the Dorsal root easing to the spinal chord
Then have short axon connecting to other neurones in CNS
Conducts action potentials from the CNS to effectors
Motor neurone in pic has myelinated axon - normally have myelinated axon
Cell body within CNS
Somatic nervous system is concerned with conscious or voluntary control
e.g. sending signals to skeletal muscles
Autonomic nervous system is concerned with controlling effectors that are involuntary or not under conscious control
E.g. cardiac muscle, smooth muscle of gut & blood vessels
Neurones tend to be non-myelinated - speed not essential
Autonomic means self-governing
2 neurones are involved pre & post ganglionic neurone - a ganglion is a small swelling
splits further into sympathetic & parasympathetic nervous systems (see above)
sympathetic nerbous system
Parasympathetic nervous system*
'fight & flight'
'rest & digest'
includes some of the cranial nerves, most importantly the vagus nerve and spinal nerves arising from the sacral region of the spinal cord.
structure of ANS
Each ganglion connects to the spinal cord in the thoracic and lumbar regions and to the internal organs
The ganglions are swellings containing cell bodies.
The structure of the ANS:- Double chain of ganglionated cords extending from the base of skull to the pelvis, one on each side of the vertebral column
ANS motor neurones which arise from the spinal cord are called pre-ganglionic neurones. They then synapse with a second set of motor neurones called post ganglionic neurones
Important to note the pre and post ganglionic neurones.
In the SNS the ganglions are outside the spinal cord
in PNS the ganglions are inside the effector tissue
In all of the pre-ganglionic motor neurones of both SNS and PSNS, ACh is the transmitter which flows across the synapse and binds with receptor sites on the membrane of the post ganglionic motor neurone
Most sympathetic motor neurones release transmitter Noradrenaline
Most parasympathetic motor neurones release transmitter Ach
These transmitters diffuse across synapses and bind with respective receptors on the CSM of the muscle tissues and gland tissues
Responses that don’t processing by the brain
Very rapid - to escape danger or avoid damage
Stimulus —> receptor —> sensory neurone —> relay neurone —> motor neurone —> effector
Info may still be sent to brain but this is to inform it of what has happen the brain isn’t making a decision
blinking reflex
There is a cranial reflex cause it uses part of the brain but ones that involve processing by the higher centres of the brain
Protects the eye
The receptor & effector are in the same place (eye area) so we call it a reflex arc
It can be triggered by:
Object touching the eye
Bright light
Loud sounds
Sudden movement near the eye
pathway:
Sensory neurone —> pons (brain stem) —> relay neurone —> motor neurone —> facial muscles
Very fast 0.1 secs from stimulus to response
Possible that higher centres of the brain a can override he reflex. You can resist blinking if you choose, inhibitory signals are sent to the motor centre in the Pons
Inputs & outputs to higher centres use myelinated neurones. This is important so that the motor neurone can be overridden in time
optical reflex
Bright light on the retina results in impulses being sent to the optical centre in the cerebrum via optic nerve
impulses return to iris muscle via oculomotor neurone & pupil constricts
knee jerk reflex
Spinal reflex
Only 2 neurones re involved (no relay neurone)
Very fast cause there is 1 less synapse
Cause there is no relay neurone the brain cannot overuse the reflex
Receptor is a muscle spindle
effects
pupils dilate
Allows more light into the eyes
Retina more sensitive to light
heart rate increases
Higher rate & pressure
Faster deliveries of glucose & O2 to muscles
CO2 removed from muscles at higher rate
Vasoconstriction & vasodilation
Blood glucose level increase
Diverts bloods away from skin & gut to your muscles
Arterioles in liver & muscles dilate
Supplies energy for muscle contraction
metabolic rate increases
Converts glucose to stable fro mod energy such as ATP
Reactor pili muscles contract
Makes hair stand up, sign of aggression & can make some mammals look bigger
breathing rate increases in rate & depth
Increases gaseous exchange so more O2 enters blood & supplies aerobic respiration
endorphins realeased
Natural painkillers realised so if you are wounded you can still continue your activity
co-ordination
1) Sensory info describing the threat is sent to cerebrum
E.g. sight, sound, smell, pain —> primary sensory areas
2) Info sent to association areas in cerebrum to integrate/make sense of what is happening
3) If threat is recognises the hypothalamus is stimulated
4) Hypothalamus increases activity in the SNS & simulates release of hormones from Anterior Pituitary gland
5) The SNS is activated to ensure a fast response
6) Nervous stimulation of the adrenal gland releases adrenaline from adrenal medulla to ensure a sustained fight r flight response
adrenaline:
The sympathetic nervous system also sends nervous signals to the adrenal medulla, instructing it to secrete adrenaline.
Adrenaline now circulates in the blood to prolong the fight or flight response
adreanal gland recap:
Adrenaline (epinephrine) will be released from the Adrenal Medulla. Adrenaline will cause the following events to continue for a prolonged period
- Relax smooth muscle in bronchioles
- Increase stroke volume of heart
- Increase heart rate
- Vasoconstriction (general) to increase blood pressure
- stimulates conversion of glycogen to glucose
- Dilates pupils
- Increase mental awareness
- Inhibits gut action
- Body hairs stand erect
how it targets cells:
Binds to receptors on CSM
G protein stimulated which activates the enzyme adenyl cyclase
Adenyl cyclase converts ATP to cAMP (cyclic AMP = 2nd messenger)
cAMP activates various enzymes inside the cell to change its behaviour
hormonal control of fight or flight
1) Hypothalamus secretes releasing hormones (CRH) into the blood
2) These pass down a portal vessel to the Anterior Pituitary gland (APG) & stimulate the release of tropic hormones (ACTH) from APG
3) ACTH causes the adrenal cortex to release Corticosteroids (e.g. Cortisol). Which regulates carbohydrate metabolism to make sure more glycogen is broken down into glucose (glycogenolysis) & also promotes glucogenesis
4) Hypothalamus also releases Thyrotropin releasing hormone (TRH)
5) This causes the release of thyroid - stimulating hormone (TSH)
6) TSH stimulates the thyroids gland to realise more thyroxine. This makes nearly every cell increase its metabolic rate
nervous control of the heart
baroreceptors
- detect pressure,
- found in aorta, vena cava & carotid artery
chemoreceptors
- Monitoring CO2, O2 & pH
- Found in aorta, Carotid artery & medulla
- Impulses pass to the cardiovascular control centre (CCC) via sensory neurones
- The CCC will send impulses to the SAN along motor neurones
response to high blood pressure
Baroreceptors stimulated
Sensory neurones to CCC (medulla)
Impulses down parasympathetic neurones (vagus nerve) to inhibit the SAN
ACH released at SAN - heart rate slows & bp brought back to normal
response to low blood pressure
Baroreceptors detect the change
Sensory neurones to CC (medulla)
Impulses down Sympathetic neurones (accelerator)
Secrete noradrenaline, binds to receptors in SAN - heart relate increases & bp brought back to normal
Simple summary of flight or flight responce
Adrenaline erased by adrenal medulla
Adrenaline can increase frequency of impulses by sino atrial node thus increasing heart rate
Adrenaline binds to adenylyl Cyclase which converts AATP to cAMP which activates hormones to convert glycogen to glucose. Glucose as requires to increase respiration for muscle contraction
SNS activated by hypothalamus which relaxes smooth muscle in airway for more O2. Dilates pupils for better vision, etc…
Hypothalamus also activates adrenals-cortical system to realise ACTH from pituitary gland which can cause release of many hormones from adrenal cortex