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)

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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

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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

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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…

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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

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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

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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

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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:

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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

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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

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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