- Created by: bethanw101602
- Created on: 02-07-18 21:43
The Nervous System
The nervous system: specialised network of cells in the human body and is our primary internal communication system.
Two main functions are:
To collect, process and respond to environmental information.
To coordinate the working of different organs and cells in the body.
Divided into subsystems:
- Central nervous system (brain and spinal Chrord)
- Peripheral Nervous system
- Autonomic Nervous system ( sympathetic and parasympathetic)
- Somatic Nervous system
Central Nervous System (CNS)
Made up of the brain and spinal cord.
The cerebral cortex (outer layer) is highly developed and distinguishes us from other animals.
Spinal cord is responsible for reflex actions.
Passes messages to and from the brain and connects nerves to the PNS.
Peripheral Nervous System (PNS)
Transmits messages, via neurons
PNS is divided into:
- Autonomic nervous system (ANS) which governs vital functions in the body e.g. breathing and stress responses.
- Somatic nervous system (SNS) which controls muscle movement and receives information from sensory receptors
Autonomic Nervous system is further split into to other proces systems:
> sympathetic nervous system ( controlls fight or flight)
> parasympathetic nervous system (regulates body after fight or flight - rest and retreat)
The Endocrine System
The endocrine system: works alongside the nervous system to control vital functions in the body via hormones.
Works slower than nervous system but it is widespread and has powerful effects.
Glands are organs in the body that produce hormones
Major endocrine gland is the pituitary gland (‘master gland’). It controls the release of hormones from all the other endocrine glands in the body.
Hormones are secreted into the bloodstream and affect any cell in the body that has a receptor for that hormone.
Thyroxine produced by the thyroid gland affects cells in the heart and cells throughout the body which increase metabolic rates (affects growth rates).
Endocrine system and ANS combining
Endocrine & ANS work together (fight or flight)
When a stressor is perceived, the hypothalamus triggers activity in the sympathetic branch of the ANS. It changes from its normal resting state (parasympathetic state) to the physiologically aroused sympathetic state.
Adrenaline is released from the adrenal medulla into the bloodstream.
Adrenaline triggers physiological changes in target organs in the body. This is called the fight or flight response.
Once the threat has passed the parasympathetic nervous system returns the body to its resting state (rest and digest).
Neurons transmit signals electrically and chemically and provide the nervous system with its primary means of communication.
Three types of neurons:
MOTOR NEURONS connect the CNS to effectors e.g. muscles and glands. They have short dendrites and long axons.
SENSORY NEURONS carry message from the PNS to the CNS. They have long dendrites and short axons.
RELAY NEURONS connect sensory neurons to motor or other relay neurons. They have short dendrites and short axons.
Structure of Neurones
Cell body (soma) includes which contains the genetic material of the cell.
Dendrites are branch-like structures that protrude from the cell body. These carry nerve impulses from neighbouring neurons towards the cell body.
Axons carry electrical impulses away from the cell body down the length of the neuron.
Covered in a fatty layer of myelin sheath that protects the axons.
Gaps in the axons called nodes of Ranvier speed up the transmission of the impulse.
Terminal buttons at the end of the axon communicate with the next neuron in the chain across a gap called the synapse.
Activation of Neurone
When a neuron is activated the inside of the cell becomes positively charged (negative when in resting state) causing action potential to occur. This creates an electrical impulse that travels down the axon towards the end of the neuron.
Synapse: the tiny gap separating neurons.
Signals within neurons are transmitted electrically and signals between neurons are transmitted chemically across the synapse.
When the electrical impulse reaches the presynaptic terminal, it triggers the release of neurotransmitter from synaptic vesicles (tiny sacs). Once the neurotransmitter crosses the gap it is taken up by the postsynaptic receptor site on the next neuron. The chemical message is converted back into an electrical impulse and the process of electric transmission begins.
Neurotransmitters have their own specific molecular structure that fits into a postsynaptic receptor site lock and key
EXCITATORY EFFECT: Increase positive the charge of the postsynaptic neuron making it more likely the neuron will fire e.g. adrenaline.
INHIBITORY EFFECT: Increasing the negative charge of the postsynaptic neuron, making it less likely the neuron will fire.
fMRI (functional magnetic resonance imaging) detects changes in blood oxygenation and flow that occurs due to neural activity in specific areas
more active brain area = more oxygen consumed and blood flow is directed to the active area (HAEMODYNAMIC response)
it produces 3D images showing which parts of the brain are active and therefore must be involved mental processes
Strength = non-invasive
Limitation = expensive
EEG (electroencephalogram) meausres electrical activity within the brain via electrodes using a skull cap.
Recordings represents the brainwave patterns generated from millions of neurons -> overall brain activity
Used as a diagnostic tool e.g. arrhythmic patters of brain activity may indicate abnormalities such as epilepsy, tumours or sleep disorders.
Strength = invaluable in diagnosing conditions
Limitation = Information is received from many thousands of neurons (difficult to distinguish)
ERPs (event-related potentials) are what is left when all extraneous brain activity from a EEG recording is filtered. (strengthens EEGs)
Done using a statistical technique – leaving those responses that relate to the presentation of a specific stimulus of performance of a certain task.
ERPs are types of brainwaves that are triggered by events.
Research has revealed many different forms of ERPs and how these are linked cognitive processes (e.g. attention and perception)
Strength = very specific measurement of neural processes
Limitation = lack of standardisation in methodology between studies
Post Mortem Examinations
Post-mortem examinations involve the analysis of a person’s brain following their death.
Areas of the brain are examined to establish the likely cause of a deficit or disorder that the person suffered in life.
This may also involve comparison with a neurotypical brain in order to assess the extent of the different.
Strength = provided the foundation for understanding the brain (Broca and Wernicke)
Limitation = causation may be an issue.
Localisation of function #1
- located- back of frontal cortex
- role- send signals from brain to motor neurones to control motor activity
- located- next to motor cortex, slightly below
- role-respond to sendsory signals from body
- located-at occipital lobe, near base of cranium
- role- transmit visual info into sight
- located- near ear, one in each hemisphere
- role- trasnmit info about sound and location
Localisation of Function #2
- located- left temporal lobe
- role-coordinate speech production
- located- behind left temporal lobe in superior lobe
- role- process meaning of speech
Case of Phineas Gage
On railroad in 1848, Gage tried to blast rock, accidentally ignite, hurled a metre length pole through his left cheek, behind his left eye, exiting his cranium from the top of his head (took a portion of his brain with it). He survived, but his personality whent from mild and well-mannered to rude and angry. Suggests frontal lobe is responsible for regulationg mood. Supports lateralisation of function theory.
Lateralisation is the idea that the two halves of the brain are functionally different and that each hemisphere has functional specialisations, e.g. the left is dominant for language, and the right excels at visual motor tasks. The Hemisphers are contrallaterol.
The two hemispheres are connected through nerve fibres called the corpus callosum, which facilitate interhemispheric communication: allowing the left and right hemispheres to ‘talk to’ one another.
Sperry and Gazzinga 1: describe what you see
- presented commissurotomy (cut corpus collosum) patients with images on eithe L or R visual field
- Found patient could describe when in R Vis Field but couldnt describe in L Vis Field
- ; The LVF is in the R hemisphere, which after the procedure has no broccas region, so couldnt describe,
- The RVF is in the L hemisphere, sp has a brocas region so can describe
Hemispheric Lateralisation #2
Sperry and Gazzinga 2: describe what you feel
- objecr placed in either L or R hand
- when object was in L hand, ptp could not describe, but could identify the feeling of similar objects (R hemisphere so not brocca)
- when object in R hand, ptp could describe and also identify similar objects (L hemisphere so has brocca)
Sperry and Gazzinga 3: draw what you see
- picture resented in either L or R VF
- Right hand couldnt draw the picture very well, as the L hemisphere is inferiro in motor tasks
- L hand could draw pictures better than right hand as R hemisphere is superior in motor tasks
- -Is ethical; cut corpus collosum was done to help epilepsy
- Supported by Brocca's findings
- case study, so small smaple size so harder to generalise
- while it was supoted by Brocca, Labourgne was dead, so cant fully explore hemisopheric lateralisation
The brains ability to modify its own structure and function as a resault of experiences. There are 3 main ways the brain can replace axon function:
- Increased brain stimulation: when neurines are damaged, neighboring neurones dont have output, so when stimulated, recovery increases
- Axon sprouting: new axons sprout from cell body to connectto nearby neurones
- Denervation super-sensitivy (DSS): axons that do a similar job will work to a higher level to compensate for the lost neurone
Functional Recovery: the brain learning to use the components availible to it to compensate for damaged areas. Two main factors can affect functional recovery:
- Age: the brain deteriorates with old age, so there is less change of functional recovery
- Gender: resaech suggests women recover better than men from brain injury as their function is not as lateralised (concentration in 1 hemisphere)
Corkin found that the right hemisphere had compensated more than the left following brain injury, but not fully. This shows hemispheric lateralisation can be compensated to a basic degree by the non-specific hemisphere.
- a pattern of behaviour that occurs every 24 hours (set and re-set by light)
- Sleep cycle every 24 hours
- Morgan: bred hampsters to have 20 hr sleep cycles
- pattern of behaviour that occurs less than every 24 hours
- can be weekly, monthly or annulally
- menstruation and the male thermal cycle
- Russell: sweat of women on others lips, menstral cycle becoam synchronised
- pattern of behviour that takes less than 24 hours to complete
- sleep is again example, but different, the stages of sleep occure more than once a aday ( we slip in aand out of REM and deep sleep multiple times evry time we sleep)
- Dann: ultradian rhythms are corelatd animal size- bigger animal= longer cycle
Exogenous Pacemakers and Endogenous zeitgebers
Suprachiastmatic nucleus (SCN) causes pineal gland to release melatonin (when optic nerve reduces activity), causes sleepy.
Siffre: cave study, shows body clock maintains sleep/wake cycle in absence of exogenous cues.
Entraiment: internal body clock is entrained by external factors. Key factor for sleep wake cycle is light intensity. Social cues are also endogenous zeitgeber such as saying good night and brushing teeth
- many studies that support use artifical light so lacks ecological validity
+ research has led to developments in shift workers