1. Structure of the Nervous System

• Central Nervous System (CNS)

  • Composed of the brain and spinal cord

  • Processes sensory information from PNS and sends motor commands back out

• Peripheral Nervous System (PNS)

  • Comprises nerves outside the CNS

  • Divided into two main divisions:

    • Somatic Nervous System

      • Controls voluntary muscle movements

      • Carries sensory information to CNS

    • Autonomic Nervous System (ANS)

      • Regulates involuntary body functions

      • Subdivided into:

        • Sympathetic Nervous System

          • Prepares body for fight-or-flight response

        • Parasympathetic Nervous System

          • Calms the body and maintains homeostasis

2. Features of Neurons

• Definition: Neurons are specialized cells responsible for receiving, transmitting, and processing information.

• Structure:

  • Dendrites: Receive signals from other neurons.

  • Cell Body (Soma): Contains the nucleus and integrates incoming signals.

  • Axon: Transmits impulses away from the cell body.

  • Axon Terminals: Release neurotransmitters into the synapse.

  • Myelin Sheath: Insulates axon, increasing impulse speed.

• Types of Neurons:

  • Motor Neurons: Transmit impulses from CNS to muscles and glands.

  • Sensory Neurons: Carry sensory information to CNS.

  • Interneurons: Relay messages between sensory and motor neurons.

    

3. Neural Transmission

• Process:

  • Action potentials travel in one direction from dendrites to axon terminals.

  • At axon terminals, neurotransmitters are released into the synaptic cleft.

• Electro-Chemical Signal:

  • Action potentials = electrical signals within neurons.

  • Neurotransmitters = chemical signals between neurons.

• Synapse:

  • Junction between pre-synaptic and post-synaptic neurons.

  • Converts electrical impulses into chemical signals and back.

4. Brain Structure and Functions

• Hindbrain: Controls basic autonomic functions; includes medulla (heart rate, breathing). Controls voluntary muscle movements; includes cerebellum (balance, coordination, swallowing). At base of brain, back of skull.

  • Medulla:

    • At base of brain stem. Front of Cerebellum.

    • Relays information between spinal cord and brain.

    • Regulates vital voluntary bodily functions (coughing, sneezing, blood pressure).

    • Damage = interruptions between brain and spinal cord. Can be fatal, as medulla controls vital organs.

  • Cerebellum:

    • Behind brainstem, beneath occiptal and temporal lobes.

    • Assist in coordinating voluntary movement and balance by relaying motor information to/from cerebral cortex.

    • Involved in balance, judging distance, coordination of fine motor movements.

    • Damage = reduced motor control, difficulty in balance, maintaining equilibrium.

    • Affected by alcohol.

• Midbrain: Involved in processing information related to hearing, vision, and movement; contains reticular formation (attention and arousal).

  • Reticular formation:

    • Throughout brainstem, from spinal cord to midbrain.

    • Stimulates brain with bombarding of sensory information - keeps cerebral cortex active and alert.

    • Controls physiological awareness and muscle tone by regulating function of ANS (sleep/wake cycle).

    • Damage = disruption to cleep/wake cycle, loss of attention, pain management and balance.

• Forebrain: Largest brain region; responsible for complex functions including cognition and emotion; includes cerebral cortex and structures like hypothalamus and thalamus.

  • Cerebrum:

    • Largest part of brain, consists of white matter (myelinated axons), cerebral cortex (grey matter; dendrites, unmyelinated axons, cell bodies of neurons).

    • Outer layer = cerebral cortex. Responsible for higher cognitive functions, voluntary movement, emotions + personality.

    • Split into two cerebral hemispheres.

  • Thalamus:

    • Two small egg-shaped structures joined together. One at top of brain, one at top of brainstem.

    • Thalamus receives all information (except smell) on way to cerebral cortex. Information travels up spinal cord and to thalamus.

    • Conducts motor signals and relays information from brainstem to cortex.

    • Coordinates shifts in consciousness.

    • Damage = loss of senses, issues with movement or tremors, attention problems, etc.

  • Hypothalamus:

    • Peanut-sized structure.

    • Located below thalamus.

    • Maintains homeostasis, regulates hormone release (connected to endocrine system); hunger/thirst.

    • Controls ‘body-clock’, assists with sleep/wake cycle.

    • Damage = disruption in body temperature regulation, growth, eating habits, weight control, emotions, sexual behaviour, motivation and sleep cycles.

4.1 Cerebral Cortex

• At surface of brain.

• Damage = problems with cognition, sensation, movement, behaviour.

• Two hemispheres:

  • Left (intellect) = verbal, analytical functions; writing, speaking, understanding. Mathematics, judging time, rhythm.

  • Right (creativity) = information processing, detecting/expressing emotion, non-verbal communication; jokes, irony, spacial/visual skills.

• Hemispheric specialisation, contralateral control of body.

• Corpus Callosum:

  • Longitudinal fissure of a thick band of nerve fibres connecting hemispheres.

  • Physically connects hemispheres.

  • Transmits information.

  • 

• Divided into four lobes:

  • Frontal Lobe: reasoning, planning, movement, emotions, and personality.

    • Primary motor cortex:

      • Rear of frontal lobe.

      • Directs skeletal muscles ~ voluntary movement (left/right - contralateral control).

      • 

    • Broca’s area:

      • Production of articulate speech.

      • Left frontal lobe, near primary motor cortex.

      • Controls respiration muscles, cheeks, lips, jaws, tongue.

      • Sentence structure, grammar.

      • Related to Wernicke’s area.

      • Damage = Broca’s aphasia, can understand, can’t produce (Broca’s broken speech).

      • 

  • Parietal Lobe: Processing sensory information; spatial awareness.

    • Somatic sensations.

    • Spatial awareness.

    • Perception of location, movement of body parts.

    • Integration of sensory language.

    • Sensory cortex:

      • Strip of neurons at front of parietal lobe, next to primary motor cortex.

      • Registers, processes sensations detected by body’s sensory receptors.

      • Contralateral reception.

  • Temporal Lobe: Auditory processing; memory formation; understanding language.

    • Understanding speech.

    • Audio information interpretation.

    • Smell processing.

    • Facial recognition.

    • Long-term memory formation.

    • Primary auditory cortex:

      • Registers, processes auditory information; left is verbal, right is non-verbal.

      • Contribute to memory via link to hippocampus.

      • 

    • Wernicke’s area:

      • Left temporal lobe, near primary cortex.

      • Identifying sounds to comprehend meaning.

      • Accesses words in memory, controlling comprehension of speech and formulation of meaningful sentences.

      • Connections to Broca’s area, left temporal lobes receiving sound. Also speech registered in primary auditory cortex of both hemispheres.

      • Damage = Wernicke’s aphasia; can speak fluently but does not make sense. Difficulty in communication. Can see and pronounce but not understand.

      • 

  • Occipital Lobe: Visual processing, facial recognition, perception of distance/depth.

    • Information from each eye is transmitted to primary visual cortex in left occiptal lobe, vice versa.

    • Primary visual cortex:

      • Processes visual information (into whole image or pattern, given meaning) from retinas via optic nerve, then send to other brain lobes.

      • Contains variety of neurons (specialised response neurons; specific to colour, shape, motion, etc.).

      • 

4.2 Localisation of Functions

• Broca’s Area: Speech production.

• Wernicke’s Area: Language comprehension.

5. Historical Studies

• Phineas Gage:

  • Case study illustrating the relationship between brain injury and personality changes.

  • Suffered a severe injury when a metal rod penetrated his skull, damaging the frontal lobe.

  • Post-accident changes included:

    • Personality shift: Became impulsive, irritable, and irresponsible.

    • Inability to hold down a job or maintain social relationships.

  • Demonstrated the role of the frontal lobe in regulating personality and social behavior.

• Roger Sperry:

  • Conducted studies on split-brain patients to explore the functions of cerebral hemispheres.

  • Findings indicated lateralization of brain functions, with each hemisphere specializing in certain tasks.

  • Highlighted how brain function is localized, impacting cognition and behavior.

• Walter Freeman:

  • Pioneered frontal lobotomies as a treatment for mental illness.

  • His methods raised significant ethical questions regarding neuropsychological treatments.

  • Conducted thousands of lobotomies, often without proper consent, leading to questions about patient rights and treatment efficacy.

6. Contemporary Methods of Study

EEG (Electroencephalogram)

• How it Works: Measures electrical activity in the brain via electrodes attached to the scalp. It detects voltage fluctuations resulting from ionic current flows within the neurons.

• Strengths: High temporal resolution allows for the measurement of brain activity in real time, making it effective for tracking dynamic changes in brain activity.

• Limitations: Low spatial accuracy; does not pinpoint the exact location of brain activity, limiting detailed brain mapping.

• Uses:

  • Diagnose epilepsy, seizure disorders.

  • Sleep research

CT (Computed Tomography)

• How it Works: Uses X-rays to create detailed cross-sectional images (slices) of the brain. A computer combines these images to provide a comprehensive view of brain structure.

• Strengths: Useful for quickly detecting brain injuries, tumors, and bleeding; widely available and fast.

• Limitations: Exposure to ionizing radiation can pose risks, and less effective in differentiating between types of soft tissues compared to MRI.

• Uses:

  • Fractures.

  • Diagnose brain tumours, aneurysms.

  • Measure size of brain tumour.

  • Assess brain injury.

MRI (Magnetic Resonance Imaging)

• How it Works: Utilizes strong magnetic fields and radio waves to generate detailed images of brain structures by aligning hydrogen atoms in water molecules and detecting their signals.

• Strengths: Provides high-resolution images with detailed structures of the brain; no ionizing radiation exposure.

• Limitations: More expensive and less accessible than CT; takes longer to conduct, and some patients may find the enclosed space uncomfortable.

• Uses:

  • Diagnose brain tumours, aneurysms.

  • Measure size of brain tumour.

  • Assess effects of stroke.

  • Assess brain injury.

fMRI (Functional Magnetic Resonance Imaging)

• How it Works: Measures brain activity by detecting changes in blood flow; areas of the brain that are more active receive more blood, which can be measured using MRI technology.

• Strengths: Non-invasive method that provides both structural and functional information; excellent spatial resolution allows for precise localization of brain activity.

• Limitations: Lower temporal resolution than EEG, so it cannot capture rapid brain activity changes with the same effectiveness as EEG.

• Uses:

  • Activity in brain when performing a task.

  • Plan for tumour removal surgery.

  • Detect brain activity of patients with neurological conditions such as Parkinson’s disease.

Structure of the Nervous System

1. Central Nervous System (CNS)

   • Composed of brain and spinal cord

   • Processes sensory information from PNS and sends motor commands back out

2. Peripheral Nervous System (PNS)

   • Comprises nerves outside the CNS

   • Divided into:

     • Somatic Nervous System: Controls voluntary muscle movements

     • Autonomic Nervous System (ANS): Regulates involuntary body functions (divided into Sympathetic and Parasympathetic Systems)

Features of Neurons

• Definition: Specialized cells for receiving, transmitting, and processing information

• Structure:

  • Dendrites, Cell Body (Soma), Axon, Axon Terminals, Myelin Sheath

• Types of Neurons:

  • Motor, Sensory, Interneurons

Neural Transmission

• Process: Action potentials transmit signals, neurotransmitters released in synapses

• Synapse: Junction converting electrical impulses to chemical signals

Brain Structure and Functions

1. Hindbrain: Basic autonomic functions (medulla & cerebellum)

2. Midbrain: Processes hearing, vision, movement; contains reticular formation

3. Forebrain: Largest region responsible for complex functions (cerebral cortex, thalamus, hypothalamus)

Cerebral Cortex

• Two Hemispheres:

  • Left: Analytical, language

  • Right: Creative, non-verbal

• Lobes:

  • Frontal: Reasoning, movement, Broca's area (speech production)

  • Parietal: Sensory processing, spatial awareness

  • Temporal: Auditory processing, Wernicke's area (language comprehension)

  • Occipital: Visual processing

Historical Studies

• Phineas Gage: Brain injury affecting personality

• Roger Sperry: Split-brain studies highlighting lateralization

• Walter Freeman: Ethical concerns in frontal lobotomies

Contemporary Methods of Study

• EEG: Measures electrical activity; good temporal resolution

• CT: Structural imaging using X-rays

• MRI: High-resolution imaging with no radiation

• fMRI: Detects changes in blood flow for brain activity