The Brain and The Nervous System

What is the function of the nervous system?

The nervous system detects and responds to internal and external stimuli

What are the two core divisions of the Nervous system?

The nervous system is split into two divisions:

The central nervous system which consists of the brain (enclosed in the skull) and spinal cord (vertebrae that forms the spinal column).

The peripheral nervous system which includes all the networks of peripheral nerves (spinal + cranial nerves) outside of the brain and spinal cord.

What are the two main Peripheral nervous subsystems?

Somatic: (voluntary nervous system - happens conciously) This part of the PNS controls voluntary movements of skeletal muscles and relays sensory information (touch, taste, smell and sound).

Autonomic: (involuntary nervous system - happens unconsciously) This part of the PNS controls involuntary body functions including: regulating your breathing, heart rate + contractility of the heart, digestion and energy conservation.

What are the two functional parts of the PNS?

Sensory division: carries nerve impulses from sensory receptors towards the CNS.

- Special senses: Touch, smell, taste, sound, and vision.

- Internal senses: Monitoring blood pressure, organ status, and body position

Motor division: Carries nerve impulses away from the central nervous system to effectors.

- Muscles: Skeletal muscles (for voluntary movements like walking) and smooth/cardiac muscles (for involuntary movements like your heart beating).

- Glands: Exocrine and endocrine glands (to release sweat, saliva, or hormones like adrenaline).

What are the two autonomic divisions?

Sympathetic system (fight or flight response) this is activated upon extreme stress, danger or physical exertion. Upon activation, your HR elevates as well as the contractility of the heart and energy. This activation causes peripheral vasoconstriction which diverts blood away from non-essential areas like digestion and toward major muscle groups. The adrenal glands release stress hormones like adrenaline and noradrenaline into the bloodstream.

Parasympathetic system (rest + digest) it promotes energy conservation, relaxation and digestion while reversing the fight or flight effects on the sympathetic system. It lowers the HR, reduces BP, stimulating digestion and contracting the bladder. They work in opposition to maintain stability (homeostasis).

What is the name of the deep groove that separates the right and left hemispheres of the brain?

Longitudinal cerebral fissure

What structure facilitates communication between the right and left hemispheres of the brain?

Corpus callosum

What is the outermost layer of the brain called?

Cerebral cortex

What are the ridges and grooves on the surface of the cerebral cortex called?

Gyri and sulci

What is the composition of the cerebral cortex?

A tiny strip of grey matter covering the cerebral hemispheres

What is the function of grey matter in the brain?

Processes, integrates, and transmits information

What is the deeper part of the brain that contains myelinated axons and glial cells called?

White matter

What is the role of white matter in the brain?

Connects different brain areas and links the brain to the body for fast signal transmission

What are the lobes of the brain?

Anteriorly - 1 x frontal lobe

Laterally - 2 x temporal lobes

Posteriorly - 1 x occipital lobe

Superiorly - 2 x parietal lobe

Define aphasia

Aphasia is a acquired language disorder caused by damage to parts of the brain that control speech and language affecting a person's ability to speak, understand, read and write

What is Broca's aphasia?

Broca's aphasia is a non-fluent communication disorder that impairs a person's ability to speak and write whilst language comprehension is intact.

Apraxia

It is a neurological motor speech disorder where the brain struggles to plan and coordinate the complex movements of the lips, jaw, and tongue needed for clear speech, even though the person understands language and wants to speak.

Regions of the Frontal Lobe

- Pre-frontal Cortex is responsible for executive functioning: planning, decision-making, problem solving and self-control as well as personality, emotional and impulse regulation.

- Broca's region is located on the left hemisphere of the frontal lobe. It converts thoughts of words into a program of muscle movements for either the muscles of the mouth and throat to produce speech.

- Motor Association Area pre-plans muscle contractions and sends information to the primary motor cortex and the supplementary cortex.

- Primary Motor Cortex is responsible for sending information to execute movements of the whole body from the lips to the movement of arms and legs

What is Wernicke's Area responsible for?

Language comprehension

Where is Wernicke's Area located?

Left hemisphere of the temporal lobe

What is the function of the Primary Auditory Cortex?

it is responsible for hearing. It helps to segment sounds into individual component sources. It also helps to localise sound sources and frequencies.

What does the Auditory Association Area process?

Auditory information including speech, music, or other sounds

What is the primary site involved with the interpretation of the sensation of taste?

Primary Gustatory Cortex

Where is the Primary Somatosensory Cortex located?

In the postcentral gyrus

What sensations does the Primary Somatosensory Cortex process?

Tactile sensations including pressure, touch, pain, and temperature

What is does the Somatosensory Association Cortex assist with?

Integration and interpretation of sensations relative to body position and orientation in space (proprioception)

Clinical Features that pt's might present with Broca's aphasia?

- Intact comprehension of auditory input and writing

- Laboured and halting speech: speaking requires great and physical effort with frequent pauses, starts and stops.

- Word finding difficulties

- Perseverance: Uncontrollable repetition of a behaviour, thought or word.

What are the regions in the occipital lobe?

- Primary Visual Cortex is the primary area of the brain responsible for sight, light, recognition, colour and dimensions

- Visual Association Area is the complex processing of visual information obtained via the primary visual cortex

What is the homunculus?

The Latin word homunculus is translated to "little man". It is a distorted, neurological map like representation of the areas and portion of the human brain dedicated to processing sensory and motor functions resulting in disproportion.

Clinical Features pt's might present with Wernicke's aphasia?

- Reduced comprehension both spoken and written

- Unable to self-monitor/ poor insight

- Mirrors speech - letters are well formed but meaningless

- Fluent speech with good intonation and articulation

What is the neurobiology model of language?

Wernicke-Licht Heim-Geschwind (WLG) is a neurological model of language. He distinctly divided areas of the brain into language production and comprehension. Broca's = left frontal lobe (language production) Wernicke's = left temporal lobe (language comprehension)

Arcuate fasciculus: Facilitates change information between these two areas. Led to the Locationist view of aphasia classification (Boston classification).

What are the limitations of the WLG model

- Assumes single word processing-

- Neuroimaging showed that there were shared areas of the brain for listening and speaking for similar syntactic structures.

- Neuroimaging studies have shown that the division of work is not equally distributed and may involve homologous areas in the right hemisphere (the left and right frontal lobes can sometimes take over functions if one side is damaged)

- Does not explain the full clinical picture e.g. Cramazza et al 1976 found that they had patients with symptoms that could not be explained using this model. Patients with lesions in Broca's area experienced both comprehension and production difficulties.