Lecture 7: Nervous System Organization and Function of the Cerebrum

Cerebrum

Largest part of brain (top/front part) which is split into left/right hemispheres

Cerebral cortex

Outermost layer of grey matter that covers the cerebral hemispheres of the brain.

What is the cerebral cortex responsible for?

Thinking, memory, voluntary movement, conscious sensor perception

• Ex: consciously grasping a pencil; perceiving sesnsations from the skin/joints

Diencephalon

Sensory and motor relay centre involved in autonomic functions.

Brainstem

Connects cerebrum/cerebellum to spinal cord; autonomic functions and cranial nerve pathway

Cerebellum

Coordination of movement and balance

Spinal cord

Motor output, sensory input, reflexes, communication with the PNS

Grey matter

Neuronal cell bodies and supporting glial cells located on the outside of the cerebral cortex.

Deep grey matter

Basal nuclei and limbic system

Nucleus

Distinct cluster/mass of grey matter (nerve cell bodies) inside the CNS.

White matter

Myelinated neuronal axons located inside the cerebrum that transmit info based on the type of fiber.

Fiber types: commissural, association, projection

Commissural fibers

Connect the two cerebral hemispheres

• Ex: corpus callosum, anterior commissure

Association fibers

Connect regions within the same hemisphere.

• Ex: connections between Wernicke’s and Broca’s area, allowing them to communication with each other.

Projection fibers

Connect the cerebral cortex with distant CNS regions like the brainstem and spinal cord.

• Ex: internal capsule

How is the arrangement of grey/white matter different in the spinal cord?

It is reversed → grey matter inside, white matter outside.

What does the contralateral cerebrum refer to?

Each hemisphere controls/receives sensory info from the opposite side of the body.

What is the left cerebral hemisphere responsible for?

Processing motor/sensory + visual info from the right side of body.

Logical processing

Language areas

• Wernicke’s area: language comprehension

• Broca’s area: language production

Aphasia

Damage to language areas, causing difficulty understanding language (Wernicke’s) or producing speech (Broca’s).

Global aphasia → both areas damaged.

What is the right hemisphere responsible for?

Processing motor/sensory + visual info from the right side of body.

Spatial orientation and object recognition

Artistic/visual processing → like interpreting 2D drawings as 3D

Ability to recognize emotional context in speech

Lateralization

The specialization of certain functions in one hemisphere (ex: hand/eye dominance).

How is lateralization different in males and females?

Less pronounced in females due to more developed commissural pathways (corpus callosum and anterior commissure)

Corpus callosum

Large commissural fibers connecting the cerebral hemispheres

Gyri

Raised raidges/folds of the cerebral cortex

Sulci

Shallow grooves between gyri

Fissures

Deep grooves that separate the hemispheres or certain lobes

Longitudinal fissure

Separates the left and right cerebral hemispheres

Central sulcus

Separates the frontal and parietal lobes

Lateral (Sylvian) sulcus

Separates the temporal lobe from the frontal and parietal lobes

Precentral gyrus

Contains the primary motor cortex

Postcentral gyrus

Contains the primary somatosensory cortex

Features of the corticol homunculus

Large hands, lips, tongue → require more motor control/sensory procesing.

Larger head/upper limbs than trunk/lower limbs.

What would a stroke affecting the left ACA cause?

Motor/sensory deficits in the right lower limb.

What would a stroke affectng the right MCA cause?

Motor/sensory deficits in left face and left upper limb.

Premotor cortex

Plans movements before execution

Located in the frontal lobe

Primary motor cortex

Executes voluntary movement

Located in the frontal lobe

Where are the premotor cortex and primary motor cortex located?

Frontal lobe

What is the frontal lobe responsible for?

Movement planning and execution → contains premotor cortex and primary motor cortex

Intellect → thinking, reasoning, morals, personality, ethics

Frontal eye field → conscious, coordinated movement of the eye

Language production → contains Broca’s area

Primary somatosensory cortex

Consciously processes general body sensations (touch, pressure, temp, pain, vibration) but not special senses!

Located in the postcentral gyrus of the parietal lobe.

Association cortex

Stores/interprets somatosensory information

Located in all lobes

Common integrative area

Combines general body sensations, special senses, and other sensory info to create an integrated understanding of the environment.

Located in parietal lobe

What is the parietal lobe responsible for?

Spatial awareness, body orientation, object recognition → contains associate cortex and common integrative area.

Processes general sensory info → contains primary somatosensory cortex

Auditory cortex

Processes and interprets info from ears (conscious perception of sound)

Located in temporal lobe

What is the temporal lobe resposible for?

Auditory processing → contains auditory cortex and association cortex

Memory storage → contains hippocampus

Language comprehension (written/oral) → contains Wernicke’s area

Visual cortex

Processes visual information → conscious perception of the field

Located in occipital lobe

What is the occipital lobe responsible for?

Visual processing → vontains auditory cortex and association cortex

Functions of basal nuclei

Deep collections of grey matter that:

• Initiates/terminates motor movements and eliminates unnecessary movements.

• Involved in procedural memory (learned subconscious habits/skills)

• Involved in attention, memory, planning, initiation/termination of cognitive processes, regulation of some emotional behaviours.

Striatum

Largest structure and main input station of the basal nuclei

Contain caudate nucleus and putamen

Steps in motor planning

1. Prefrontal cortex plans an intended movement.

2. Prefrontal cortex communicates with basal nuclei to access learned motor routines.

3. The info passes through the thalamus before returning to the cortex.

Allows the cortex to use rapidly use established movement patterns.

Substantia nigra

Dark-pigmented nucleus located in the midbrain, containing dopamine-producing neurons.

Role of dopamine in the nigrostriatal pathway

Dopamine is released in the substantia nigra and sent to the basal uclei to regulate intiation/termination of movement.

Cause of Parkinson’s disease and its symptoms

Loss of dopamine-producing neurons in the substantia nigra → inhibits basal nuclei function → difficulty initiating/terminating movements. 

Cause of Huntington’s chorea and its symptoms

Neurodegeneration in the striatum → excessive involuntary movements

Function of the limbic system

Emotional and memory center of the brain, involved in:

• Memory formation

• Emotional processing

• Responses to significant stimuli

Structures in the limbic system

Hippocampus, entorhinal cortex, amygdala, mammillary bodies, fornix, cingulate cortex.

Function of the hippocampus

Encording and consolidating memories (organize info about who, what, where, when)

Encoding

First step in memory processing → transforms incoming info and neural activity into a form that can be stored/retrieved later

Consolidation

1. Integrating different components of an experience (sight, smell, etc)

   • All somatic sessations and special senses must pass through the hippocampus.

2. Stabilization of memories of long-term storage

Entorhinal cortex

Brain’s “GPS” → spatial memory and navigation; helps associate memories with spatial/contextual info

Located in the temporal lobe

Function of the amygdala

Subconsciously assesses potential threats

Produces fear responses by communicating with the hypothalamus to influence autonomic function (activation of SNS → dilated pupils, muscle trembling, sweating, faster heart rate)

Interpret fear/anger in other people

Add emotional signifiance to memories

How does alcohol affect the amydala?

Impairs its ability for threat assessment/analysis, leading to risky behaviours.

Disordered amygdala function may lead to

Anxiety-related disorders

Function of mammillary bodies

Participate in memory processing by linking sensory experiences (especially smell) and emotions to memories.

Which pathway are mammillary bodies connected to?

Olfactory

Fornix

Major fiber pathway → mammillary bodies receive input from hippcampus via fornix.

Cingulate cortex

C-shaped region that wraps around the corpus callosum

Declarative memory

Conscious, intentional recollection of facts, events, and specific information.

Two types of declarative memory

1. Semantic memory

2. Episodic memory

Semantic memory

Memory for facts and general knowledge

Episodic memory

Memory for personal experiences/events

Non-declarative memory

Long-term memories that you use and store without conscious awareness

What brain regions regulate declarative memories?

Limbic system

What brain region regulates non-declarative memories?

Cerebellum, basal nuclei, thalamus

Role of cerebellum in non-declarative memories

Learning new motor proecdures

Pathway for learning new motor procedures

Sensory info → cerebellum → thalamus → premotor cortex

Role of basal nuclei in non-declarative memories

Develop and execute familiar motor routines → help movements become automatic through repeated experience.

Pathway for familiar motor movements

Early experience → basal nuclei → thalamus → premotor cortex

Role of thalamus in non-declarative memories

Regulates ability to switch between the:

• Cerebellum, when adjusting movement in response to changing sensory info.

• Basal nuclei, when executing well-learned movement routines.

Amnesia

Memory loss of facts or experience

Either anterograde or retrograde

Anterograde amnesia

Inability to form new memories

Retrograde amnesia

Loss of memories formed before brain injury

Why can anterograde vs. retrograde amnesia and declarative vs. procedural memory formation occur independently?

Different brain regions are responsible for different memory systems.