Brain Structure and Functions

Name 2 neuron functions

1. They react and respond to stimuli

2. They learn and store information about the external environment

What are neurons comprised of (structure)

Dendirites - receive incoming information

Cell body - where information is stored, it is important for cellular function

Axon - send neural information (signals) to other neurons

Name 4 types of neurons

1. Unipolar

2. Pseudounipolar

3. Bipolar

4. Multipolar

Describe 'Unipolar' neurons

Only one process originating (emanating) from the cell body

Describe 'Pseudounipolar' neurons

One process extending from the cell body, which ends up splitting into two processes.

Describe 'Bipolar' neurons

Two processes emanating from the cell body (axon and dendrites) on each side

Describe 'Multipolar' neurons

Multiple processes extend from the cell body, simultaneously

Name the 5 functions neurons possess.

1. Sensory abilities

2. Motor abilities

3. Interneurons

4. Afferent

5. Efferent

Describe the function of sensory neurons

Transmission of sensory information to the CNS

Describe the function of motor neurons

carry information from the CNS to extremities (muscles and glands)

Describe the function of interneurons neurons

They facilitate communication between sensory and motor neurons

Describe the function of afferent neurons

They carry information from sensory receptors towards the CNS

Describe the function of 'efferent' neurons

They send information away from the CNS (the brain), to the peripheral nervous system (PNS)

**in the form of motor neurons**

Describe the internal anatomy of a neuron

The neuron is encased in a plasma membrane.

- It is comprised of a phospholipid bilayer

- It is selectively permeable, which allows selected materials in and out.

It also has organelles such as the nucleus, ribosomes and mitochondria.

- Ribsomes are responsible for protein production

What are Glial cells?

Cells that provide supportive functions.

Name 3 kinds of Glia cells

1. Astrocytes

2. Oligodendrocytes

3. Microglia

What are the functions of astrocytes?

- Largest glia cell

- Regulate the chemical content of the extracellular space

- Nutritive and metabolic functions

- Help maintain the **blood-brain barrier (BBB).

What are the functions of oligodendrocytes?

Myelinate cells of the CNS, through the production of myelin (a fatty substance insulating the axon)

What are the functions of microglia?

- Smallest glia

- Remove debris, and eliminate harmful substances

Explain the process of Action Potential (Nerve impulse)

This process occurs (within) a single neuron, where information is transmitted as an electrical current (created by Na+ and K+ ions) through ion channels.

(Between) neurons that information is converted into a *chemical message*

What is the resting potential (charge) of a neuron?

-70mV, which is maintained by the sodium pump.

Describe the processes involved in action potential

1. Depolarization: Sodium is allowed into the cell.

2. Overshoot: Membrane potential peaks as sodium enters.

3. Repolarization: Sodium channels close, and potassium channels open.

4. Hyperpolarization: Potassium leave the cell, briefly causes the membrane potential to dip below the resting level.

5. Return to rest: The sodium-potassium pump actively restores the original ionic distribution.

What is the presynaptic cleft?

The gap separating presynaptic neurons (axons) and postsynaptic neurons (dendrites) where neurotransmitters are released into, following the process of action potential.

What is the name for the process of neurotransmitter release?

Exocytosis

Explain the postsynaptic effects

Once a neurotransmistter has gone across the synapti cleft, it exerts effects on the post synaptic neuron. The postsynaptic effects occur when the neurotransmitter attaches to a receptor.

Name 2 types of postsynaptic effects

1. Excitatory post-synaptic potentials (EPSPs)

2. Inhibitory post-synaptic potentials (IPSPs)

Describe excitatory post-synaptic potentials (EPSPs)

EPSPs increase the cell's positive charge.

Describe Inhibitory post-synaptic potentials (IPSPs)

IPSPs make the cell's interior more negative

What 2 types of receptors are found on the postsynaptic membrane

1. Transmitter-gated ion channels (Iontropic)

2. G-protein-coupled receptors (Metabotropic)

What does the process of terminating the action of a NT include?

1. Reuptake

2. Enzymatic deactivation

3. Glial cell degradation

4. Autoreceptor regulation

5. Diffusion

Explain the process of 'reuptake'

NTs are removed from the presynaptic cleft, and are returned back to the axon terminal

Explain the process of 'diffusion'

The NT float away, and out of range of receptors.

What are neurotransmitters (NTs)?

Chemicals released by neurons when the cell is activated by an action potential.

What are the two most prevalent neurotransmitters found in the CNS?

Excitatory and inhibitory

Describe amino acids

- Primary neurotransmitters in the CNS

- Glumate (excitatory) + GABA (gamma-aminobutyric acid)(inhibitory)

What are the four major neurotransmitter systems?

Cholinergic (e.g., Acetylcholine)

Dopaminergic (e.g.,Dopamine)

Noradrenergic (e.g., Norepinephrine, Noradrenaline

Serotonergic (e.g. Serotonin)

Define agonists

Substances that mimic or enhance a neurotransmitter's effect on target neurons

Define antagonists

Oppose or diminish the neurotransmitter's effect on neurons by binding to receptors and decreasing its impact.

Describe the cholinergic system

- Utilises ACh (Acetylcholine) as primary neurotransmitter

- Originates in the basal forebrain (additional nuclei in the pons and midbrain)

- Projects to cortical regions, affecting cortical excitability, sustained attention and memory.

- Dysfunction is associated with Alzheimer's Disease

Describe the dopaminergic system

- Dopamine as primary neurotransmitter

- Influences working memory, reward processing and attention.

- Classified into D1 and D2 famililies

- Comprised of Nigrostriatal, Mesolimbic and Mesocortical subtypes.

Describe the noradrenergic system

- Originates at the locus coeruleus (small area of the brain), and extends to the hypothalamus, thalamus and prefrontal cortex.

- It influences behaviours such as feeding, sexual behaviour, attention, sleep and working memory.

- Problems in this area may be attributed to ADHD and other attentional difficulties

Describe the serotergenic system

- Originates in the dorsal raphe nucleus, medial raphe nucleus, pons, and medulla.

- Influences areas for sleep, arousal, mood, anxiety, sexual behaviour, appetite and memory.

- SRRIs are used to tretat symptoms of depression

What is important to note about the interaction between Neurotransmitter systems?

They are highly interrelated.

Dopamine and Norafrenline are both associated with ADHD.

Serotonergic and cholinergic systems are both implacetd in long-term memory formation and sleep.

Define the terms rostral & caudal

Regions toward the front & regions toward the base of the brain (back).

Define the terms dorsal & ventral

The top part & bottom part of the brain.

What are the two major divison of the nervous system?

The central nervous system (CNS) and peripheral nervous system (PNS).

What is the CNS comprised of?

The brain (protetced by the skull) + spinal cord

What is the PNS comprised of?

Neural tissues outside the CNS, and is divided into:

- The somatic nervous system

- The autonomic nervous system = sympathetic + parasympathetic + enteric

What is the function of the spinal cord?

The transmission of sensory information from the body to the brain and motor commands from the brain to the muscles.

What are the main functions of the skull?

It encases the brain, and protects it, damage to the skull may result in brain damage.

The brain is also procted by the meninges.

Name the 3 layers which make up the meninges

1. Pia mater

2. Arachnoid mater

3. Dura mater

Describe the ventricular system

It contains CSF (cerebrospinal fluid) and is comprised of lateral, interventricular foramen, third ventricle and the cerebral aqueduct. Its purpose is to protect the brain.

What are the major arteries of the brain?

Antertior circulation (2 internal carotid arteries)

Postertior circulation (2 vertebral arterties)

Name the major divisions of the brain

- Hindbrain (Rombecephalon)

- Midbrain (Mesecencephalon)

- Forebrain (Prosencephalon)

What does the hindbrain consist of?

Myelencephalon and Metencephalon

Myelencephalon

Medulla oblongata

Describe the medulla oblongata

- Made up of 12 pairs of cranial nerves (e.g., optic nerve)

- Supports life-sustaining functions

- Damage = fatality

- Responsible for managing sensory input

- RAS (attention, arousal, consciousness (sleep-wake cycles))

Define decussation

Crossing of motor fibres (left hemisphere, controls the right side of the body, right hemisphere controls the left side of the body)

Metencephalon

Pons and Cerrebellum

Describe the pons and its functions

- Connect the cerebellum and the rest of the brain

- It serves the functions of balance, sleep-wake cycles, breathing.

Describe the cerebellum

- Guides motor activity

- Balance and coordination

- Regulation of muscle tone

Describe the tectum and its functions

Superior colliculi

- Detecting and Orientation of peripheral vision toward large, moving stimuli.

Inferior colliculus

- Head and eye movements as a reflex to sound.

Describe the tegmentum and its functions

Tegmentum

- Contains important nuclei related to motor skill and pain perception

Forebrain

Diencephalon and Telencephalon

Diencephalon

Thalamus and Hypothalamus

Describe the functions of the thalamus

Relay centre for transmitting sensory information.

Describe the functions of the hypothalamus

Small, heterogeneous nuclei that maintains homeostasis.

Homeostasis is a process for body regulation (fight or flight, body temperature regulation).

Describe the structure and functions of the basal ganglia

Motor control, and regulation of involuntary movements.

Damage to this area results in motor issues (Huntington's and Parkinson's)

Describe the structure of the limbic systems and its functions

- Amygdala (fear and anger response - emotion regulation)

- Hippocampus (memory)

Describe the structure of the cerebral cortex

- gyri (folds of the brain)

- sulci (grooves)

- It is comprised of primary, secondary and association areas of the brain

Primary area → secondary areas → association areas

Describe the functions of the primary motor cortex

Located in the frontal lobe

- Send motor related information down to the body

Describe the functions of the somatosensory cortex

Located in the parietal lobe

- First point for receiving sensory information

- Damage can result in mild to large loss of sensation

What are the 3 components of the frontal lobe?

1) Primary motor cortex

2) Premotor region

3) Prefrontal cortex

Which parts of the prefrontal cortex are worth noting?

Dorsolateral PFC- working memory and attentional processing

Orbital cortext - emotional processing

Medial PFC - judgement, decision-making and detecting errors

What are the characteristics of the frontal lobe?

- Executive functions, and its central role in planning, guiding, and evaluating behaviour

- Regulation of complex social behaviour and influence personality

- Impairment and damage may result in perseveration (repeated behaviours), disruption in organisational behaviours.

Describe the structure and functions of the parietal lobe

Made up of the superior and inferior parietal lobe

- Spatial cognition or visuospatial reasoning

Damage to this area my result with issues in reading (alexia), and writing (agraphia), spatial cognition deficits and hemispatial neglect

Describe the structure and functions of the temporal lobe

Primarily involved in language processing and memory

- damage can lead to agnosia, the inability to recognise familiar objects, sounds, or melodies, despite intact sensory function.

Describe the structure and functions of the occipital lobe

The region responsible for visual perception and processing

- Damage to this area may result in visual agnosia (a condition in which individuals are unable to recognise familiar objects visually despite intact visual perception.)