Nervous System: CNS, PNS, and Divisions

• The nervous system is a specialized network of cells, the body's main internal communication system, using electrical and chemical signals.
• The nervous system collects, processes, and responds to environmental information, coordinating organs and cells.

Divisions of the Nervous System

• The nervous system is divided into the Peripheral Nervous System (PNS) and the Central Nervous System (CNS).

Central Nervous System (CNS)

• The CNS consists of the brain and spinal cord, the origin of complex commands and decisions.

Peripheral Nervous System (PNS)

• The PNS sends information from the outside world to the CNS and transmits messages from the CNS to muscles and glands.

Somatic Nervous System (SNS)

• The SNS transmits sensory information to the CNS and receives information from the CNS that directs muscles to act voluntarily.

Autonomic Nervous System (ANS)

• The ANS transmits information to and from internal organs and operates involuntarily, controlling functions like breathing and heart rate.

ANS Divisions: Sympathetic and Parasympathetic

• The ANS divides into Sympathetic and Parasympathetic branches.

Sympathetic Nervous System

• The sympathetic nervous system triggers the "fight or flight" response, increasing heart and breathing rates, dilating pupils, inhibiting digestion and saliva production, and contracting the rectum.

Parasympathetic Nervous System

• The parasympathetic nervous system promotes "rest and digest," decreasing heart and breathing rates, constricting pupils, stimulating digestion and saliva production, and relaxing the rectum.

Application of Nervous System Functions

• The CNS processes sensory input and coordinates responses; in a frightening experience, the brain interprets threats and initiates reactions.
• The ANS, particularly its sympathetic branch, activates physiological changes like increased heart rate and sweating during fear, preparing the body for fight or flight.

Endocrine System

• The endocrine system works with the nervous system to control vital functions, acting more slowly but with widespread effects.
• Glands produce hormones, which are secreted into the bloodstream and affect cells with specific hormone receptors.

Endocrine and ANS Collaboration in Fight or Flight

• A stressful event activates the hypothalamus, which triggers the pituitary gland and sympathetic state (fight or flight), leading to the release of adrenaline from the adrenal medulla and subsequent physiological changes; the parasympathetic system then promotes rest and digest after the threat passes.

Key Endocrine Glands

• The pituitary gland, located in the brain, regulates growth, metabolism, and reproduction through hormones and is known as the master gland.
• The pineal gland secretes melatonin in response to darkness, regulating the sleep-wake cycle.
• The adrenal gland produces adrenaline, aiding the fight-or-flight response.

Neurons

• Neurons are nerve cells that process and transmit messages through electrical and chemical signals, enabling communication within the nervous system.

Soma (Cell Body)

• The soma includes a nucleus containing the cell's genetic material.

Dendrites

• Dendrites carry nerve impulses from neighboring neurons towards the cell body.

Axons

• Axons carry impulses away from the soma down the neuron's length and are covered in a myelin sheath.

Myelin Sheath

• The myelin sheath is a fatty layer that protects the axon and speeds up electrical transmission, segmented by Nodes of Ranvier.

Nodes of Ranvier

• Nodes of Ranvier speed up transmission by forcing impulses to "jump" across gaps along the axon.

Axon Terminals

• Axon terminals communicate with other neurons in the chain across a synapse.

Sensory Neurons

• Sensory neurons carry messages from the PNS to the CNS and have long dendrites and short axons.

Relay Neurons

• Relay neurons connect sensory neurons to motor or other relay neurons and have short dendrites and short axons.

Motor Neurons

• Motor neurons connect the CNS to effectors like muscles and glands and have short dendrites and long axons.

Synaptic Transmission

• Synaptic transmission is the process by which neighboring neurons communicate via chemical messages across the synapse.

Chemical Transmission

• Neurons communicate chemically across the synapse; electrical impulses trigger the release of neurotransmitters from synaptic vesicles at the presynaptic terminal.

Synapse

• The synapse is a tiny gap between neurons.

Neurotransmitters (NTs)

• Neurotransmitters are chemical messengers that diffuse across the synapse to the next neuron, fitting into postsynaptic receptor sites like a lock and key.

Neurotransmitter Process

• Neurotransmitters cross the synapse, bind to postsynaptic receptors, and convert the chemical message back into an electrical impulse, continuing the transmission process.

Axons vs. Dendrites

• Axons carry signals to the synapse, while dendrites carry signals away from the synapse.

Neurotransmitter Functions: Excitatory and Inhibitory

• Neurotransmitters are divided into those with excitatory and inhibitory functions.

Excitation and Inhibition

• Neurons at rest are negatively charged inside; activation causes a positive charge, leading to action potential.

Excitation

• Excitatory neurotransmitters, like adrenaline, increase the positive charge of the postsynaptic neuron, increasing the likelihood of passing on the electrical impulse.

Inhibition

• Inhibitory neurotransmitters, like serotonin, increase the negative charge of the postsynaptic neuron, decreasing the likelihood of passing on the electrical impulse.

Summation

• Summation determines whether a postsynaptic neuron fires.

Summation Effects

• The postsynaptic neuron is less likely to fire if the net effect is inhibitory and more likely to fire if excitatory
• Action potential is triggered only when the sum of excitatory and inhibitory signals reaches the excitation threshold.

Localisation of Function

• Different brain areas are responsible for different processes.

Holistic Function

• Brain activity is understood by the workings of the entire organ.

Brain Lobes

• The brain lobes include the frontal, parietal, temporal, and occipital lobes, plus the cerebellum and brain stem.

Areas of the Brain

• Key brain areas include Broca's area, Wernicke's area, hippocampus, amygdala, hypothalamus, limbic system, pituitary gland, motor area, somatosensory area, visual cortex, and auditory area.

Broca's Area

• Broca's area, in the frontal lobe of the left hemisphere, is responsible for speech production.

Wernicke's Area

• Wernicke's area, in the temporal lobe of the left hemisphere, encircles the auditory cortex, involved in language comprehension.

Motor Area

• The motor area, in the frontal lobe, regulates movement.

Somatosensory Area

• The somatosensory area, in the parietal lobe, processes sensory information like touch.

Visual Cortex

• The visual cortex, in the occipital lobe, processes visual information.

Auditory Area

• The auditory area, in the temporal lobe, analyzes speech-based information.

Aphasia

• Aphasia is a language disorder affecting communication, caused by damage to brain areas controlling language expression and comprehension, such as Broca's aphasia.

Lesion

• A lesion is an area of damage.

Localisation Evidence: Leborgne (Broca's patient)

• Leborgne, who could only say "tan," had a lesion in the left frontal lobe, identified by Paul Broca as responsible for speech production (Broca's area).

Localisation Evidence: Peterson

• Peterson et al. used brain scans to show Wernicke's area was active during listening tasks and Broca's area during reading tasks.

Holistic Theory Evidence: Danielli et al. (EB)

• EB, who had his left hemisphere removed at age 2 due to a tumor, had initially impaired language skills that localized on his left hemisphere.
• At 17 his right hemisphere compensated so was functioning linguistically well with only minor problems.

Holistic Theory Evidence: Lashley

• Lashley found that no single area of the cortex was more important than others in rats learning a maze route after removing areas of the cortex.

Hemispheric Lateralisation

• The two brain hemispheres have different functions, with certain mental processes and behaviors mainly controlled by one hemisphere.

Left Hemisphere Functions

• The left hemisphere handles language processing, processes detail within the visual field, and controls the right side of the body. It is known as the analyser.

Right Hemisphere Functions

• The right hemisphere can produce only basic words but provides meaning and emotional context, recognizes emotions in others, and handles overall visual patterns; it’s better for motor tasks and controls the left side of the body and is known as the synthesizer.

Corpus Callosum

• The corpus callosum is a communication pathway allowing the two hemispheres to exchange information.

Lateralisation

• Specific functions are controlled or dominated by a particular hemisphere, like language in the left hemisphere via Broca's and Wernicke's areas.

Contralateral

• Contralateral refers to the opposite side of the body, as the brain is in most people.

Ipsilateral

• Ipsilateral refers to the same side of the body.

Hemispheric Lateralisation in Activity

• The left side of the body is controlled by the right hemisphere and vice versa, demonstrating contralateral control.

Hemispheric Lateralisation in Vision

• The left visual field of both eyes is processed by the right hemisphere, and the right visual field by the left hemisphere; this is both contralateral and ipsilateral.

Hemispheric Lateralisation Evidence: Sperry

• Sperry's split-brain patient studies showed that patients could describe images shown to the right visual field (left hemisphere) but could only draw objects shown to the left visual field (right hemisphere) with their left hand.

Hemispheric Lateralisation Evidence: Brain Scans

• Brain scans indicate that tasks like language processing activate the left hemisphere, while spatial tasks activate the right hemisphere even in non-split-brain patients.

Hemispheric Lateralisation Limitation: Plasticity

• Research indicates that the remaining hemisphere can compensate for damage in one hemisphere, especially in children, showing that lateralisation can adapt.

Split Brain Research

• Split-brain research investigates the effects of severing the corpus callosum, often to treat severe epilepsy.

Sperry's Aim

• Sperry aimed to investigate of severing the corpus callosum and understand the independent functions of the brain's two hemispheres.

Sperry's Findings - Visual Tasks

• In visual tasks with images/words presented to one visual field:
• LVF (RH): unable to name objects, but could draw or select with left hand;
• RVF (LH): could verbally name objects.

Sperry's Findings - Tactile Tasks

• In tactile tasks with objects placed in one hand without looking:
• left hand (RH): unable to name object, but could recognize by touch;
• right hand (LH): could name object.

Sperry's Evaluation

• Sperry had highly controlled lab conditions.
• The study provided strong evidence for lateralisation of function.
• The used a small sample of only epilepsy patients; also, the artificial lacked mundane realism

Brain Plasticity

• Brain plasticity is the brain's ability to alter its structure and function.

Synaptic Pruning

• Frequently used brain connections strengthen, while rarely used connections weaken and are eliminated
• Synaptic pruning enables lifelong plasticity as the brain adapts and forms new connections in response to environmental demands.

Draganski's Aim

• Draganski aimed to see whether learning a new skill (juggling) would affect the brains of participants.

Draganski's Procedure

• Participants were split into juggler and control groups.
• Jugglers underwent an MRI scan before the study, then learned to juggle.
• Once jugglers mastered a routine, they had a 2nd MRI scan, then stopped juggling - After 3 months a third MRI scan was conducted
• The used VBM to analyze the MRI scans to determine neural density differences.

Draganski's Findings

• The first scans showed no differences between groups.
• The second scans found that jugglers had increased grey matter in the mid-temporal area of both hemispheres.
• Third scans revealed that areas of increased grey matter had decreased.

Maguire’s Aim

• To see whether the brains of taxi drivers would be different as a result of their exceptional knowledge of London and spending many hours driving.

Maguire’s Procedure

• The study involved 16 right-handed male London taxi drivers (+ control group)
• Participants had completed the 'knowledge' test and had their licence for at least 1.5 years.
• MRIs were used, and VBM + pixel counting were used to measure the data.

Maguire’s Findings

• Taxi drivers had significantly larger posterior hippocampi (linked to spatial navigation) and smaller anterior hippocampi.

Functional Recovery

• Functional recovery is a form of neuroplasticity, referring to how brains adapt to damage/trauma.

Brain's Response to Trauma/Damage

• The Brain is not able to regenerate, so once it is damaged neurorehabilitation is needed to compensate to work again.
• While everyone has the ability to recover, it is the degrees of recovery that differ

Neurorehabilitation

• Aims to recover damaged brains.

Individual Differences and Recovery

• Age (younger = easier recovery due to greater plasticity)
• Gender (women = sometimes greater recovery due to great lateralisation of function)
• Education (more education = easier recovery due to greater cognitive reserve).

Brain Compensation Methods

• Axonal regeneration/sprouting, denervation supersensitivity, and recruitment of homologous (similar) areas are 3 ways the brain compensate itself

Axonal Regeneration/Sprouting

• The Growth of new nerve endings connect w/ undamaged cells to form new neural pathways, attempting to repair or compensate for damage to neurons.

Denervation Supersensitivity

• Axons w/ similar jobs compensate by becoming aroused to a higher level.
• Negatively has an effect of oversensitivity to messages like pain.

Recruitment of Homologous (Similar) Areas

• Specific tasks/functions can be performed by the other side of the brain after lost due to damage
• For example, if Broca's area was damaged in the LH, the right side equivalent would carry out its functions.
• Functionality may shift to back the left after a period of time.

Brain Plasticity Strengths

• Supported by research (Maguire, Draganski, Danielli)
• Has real world applications for neurorehabilitation

Brain Plasticity Limitations

• Negative plasticity (e.g. phantom limb syndrome)
• Individual differences (Schieder et al)

Danielli et al. (EB)

• EB had his left hemisphere removed (age 2) due to a tumour
• The Language localisation was in his left, but at 17 he was functioning linguistically well with only minor problems, suggesting the case study is not necessarily generalizable

Schieder et al

• People who have greater cognitive reserve are more likely to recovery
• The study only has correlation not causation

Ways of Studying the Brain

• fMRI, EEG (electroencephalograms), ERP (event-related potentials), and post-mortems are used to study the brain.

fMRIs

• measures blood flow to detect areas of activity (more oxygen use = more active)
• used by studies such as Danielli's

fMRIs - Evaluation

• High spatial resolution and non-invasive
• Poor temporal resolution and expensive

EEGs

• Measures electrical activity using electrodes on the scalp
• Not specific, general brain activity
• Used by sleep research

EEGs Evaluation

• Excellent temporal resolution and real world application diagnosing epilepsy and sleep disorder
• Only measures surface activity and poor spatial resolution

ERPs

• Measures brain responses to specific stimuli
• Similar to EEGs but more advanced