Head & Neck 1: Brain & Structure 1

Brain

Most metabolically expensive tissue, 20% blood oxygen, 130g glucose per day, can’t store glucose

4 Divisions of Brain

1. Cerebrum

2. Diencephalon

3. Brainstem

4. Cerebellum

Cerebrum Overview

Largest part of brain (80% brain mass). Gray and white matter.

Parts:

1. L/R hemispheres

   • Gyri, sulci, fissures (cerebral cortex)

   • Corpus callosum

2. Basal Nuclei/Ganglia

Cerebrum Functions

1. Conscious thought process

2. Memory

3. Reasoning

4. Conscious and subconscious movement of skeletal muscle

Cerebral Cortex

Surface of the cerebrum made of gyri, sulci, and fissures. Gray matter. Help separate the brain.

Gyri

(Gyrus; singular) Ridges, “squishy worms”, gray matter

Sulci

(sulcus; singular) shallow depressions, “lines”, gray matter

Fissures

deeper depressions

Gray matter

Neuronal cell bodies, dendrites, unmyelinated axons, outer part of brain

Neuronal cell bodies

Part of a neuron with nucleus and organelles. Processes signals and facilitates communication throughout the nervous system.

Dendrites

Receives signals and send them towards the cell body.

Unmyelinated axons

Axons that lack a myelin sheath are found in gray matter. Slower signal transmission and process sensory and motor information.

White matter

Most of brain mass, surrounded by gray matter, myelinated axons of neurons

Longitudinal fissure

Separate left and right hemispheres of the cerebrum

Corpus Callosum

Connects left and right hemispheres of the cerebrum through commissural fibers. Allows sharing of learning and memory between hemispheres. White matter.

Commissural fibers

Tracts of neurons that cross from one brain hemisphere to the other. Makes up the corpus callosum

Transverse fissure

Separates left and right hemispheres of the cerebrum from the cerebellum

Frontal lobe

Largest, personality, thinking & reasoning. Primary motor cortex, Broca’s (speech motor). Conscious control of muscles.

Pariental lobe

Primary sensory cortex. Sensation of touch, temperature, pain, pressure, vibration, taste.

Temporal lobe

Primary auditory and olfactory cortex. Stores sound and smell.

Occipital lobe

Visual cortex. Interprets what you see

Important Sulci

Separate functional sections of the brain (lobes)

1. Central sulcus

2. Lateral sulcus

3. Parieto-occipital sulcus

Central sulcus

Separates frontal and parietal lobe

Lateral sulcus

Separates temporal from parietal and frontal lobes

Parieto-occipital sulcus

Separates occipital lobe from the rest of the brain

Important gyri

Separated by central sulcus.

1. Precentral gyrus

2. Postcentral gyrus

Precentral gyrus

Primary motor region, frontal lobe, anterior to central sulcus.

Postcentral gyrus

Primary somatosensory region (temperature, pain, pressure anywhere in body), parietal lobe, posterior to central sulcus

Homonculus

Represents motor and sensory distribution of precentral and postcentral gyrus

Nuclei

Collection of nerve cell bodies

Basal nuclei/ganglia

5 specialized paired masses of gray matter nuclei hidden deep inside sea of white matter.

Striatum:

1. Caudate nucleus

2. Putamen

3. Globus pallidus (under putamen)

4. Subthalmic nuclei: part of diencephalon

5. Substantia nigra: midbrain

Associated closely with basal nuclei/ganglia

Movement-control system. The cerebral cortex has an intended movement, and the basal nuclei helps fine-tune which skeletal muscle movement gets expressed appropriately; supresses unwanted movements. Coordination of learned movement patterns (sports, dancing). Located deep in white matter.

Caudate nucleus

Head, body and tail (ends near amygdaloid body)

Putamen

Lateral/superficial (outermost part)

Globus pallidus

Medial/deep (medial to the putamen and inferior to the caudate nucleus)

Caudate nucleus, putamen, globus pallidus transverse image

Caudate nucleus, putamen, globus pallidus coronal image

Internal Capsule

White matter between the basal nuclei/ganglia where neuronal tracks go through (projection fibers). Between caudate nucleus and putamen + globus pallidus

Descending motor tracts: go from cerebral cortex through midbrain to cerebral cortex

Ascending motor tracts: go from spinal cord through midbrain to cerebral cortex

Basal ganglia pathways

Coordinated movement of skeletal muscles. Final movement command loops through brain first before sent to skeletal muscles.

1. Cortex-to-cortex circuit (basal ganglia consulting loop)

2. Nigrostriatal (substantia nigra—>striatum) pathway

Cortex-to-cortex circuit (basal ganglia consulting loop)

Cortex—>Striatum—>Globus pallidus—>Thalamus—>Cortex—>Midbrain to spinal cord—>Muscles

Substantia nigra

Region near the midbrain involved in movement control, cognitive exectutive functioning, emotions.

1. Pars compacta: produces dopamine from neurons with neuromelanin (black)

2. Pars reticulata: eye movements and cognitive functions, produces GABA (inhibitory NT)

Nigrostriatal pathway (pars compacta)

Substantia nigra pars compacta (releases dopamine to influence…)—>Striatum

Regulates speed, direction, force of movement

Huntington’s Disease

Inherited neurodegenerative disease affecting striatum

Uncontrolled movements, memory lapses, difficulty concentrating, depression, mood swings, speech changes. Common causes of death: Falls or Aspiration pneumonia due to choking (unable to swallow properly…aspirate bacterial saliva)

Parkinson’s Disease

Progressive degeneration of dopamine producing cells in substantia nigra (black parts…neuromelanin)

Tremors, rigid limbs and torso, impaired balance, affects emotions and cognition. Aspiration pneumonia and falls.