Anatomy Unit 4: The Brain

Gyrus

An elevated fold of the brain surface. Gyri increase cortical surface area, so more cortex fits in the skull.

Sulcus

A shallow groove between gyri.

Fissure

A deep groove between gyri. Sulci are shallow and fissures are deep, so don't mix them up.

Cerebral Hemispheres

The left and right halves of the cerebrum, the largest part of the brain, separated by the longitudinal fissure.

Each hemisphere is divided into four lobes (frontal, parietal, temporal, occipital).

Each has three basic regions: cerebral cortex (outer gray matter), internal white matter, and basal nuclei (inner gray matter).

Each hemisphere manages the sensory and motor functions of the contralateral (opposite) side of the body.

Frontal lobe (mainly responsible for?)

Primarily responsible for voluntary motor control, personality, and motor speech. The most anterior cerebral lobe, separated from the parietal lobe by the central sulcus and the temporal lobe by the lateral fissure.

Contains the precentral gyrus (primary motor cortex), prefrontal cortex (personality), and Broca's area (motor speech); lies in the anterior cranial fossa.

Parietal lobe (mainly responsible for?)

Lies behind the central sulcus, between the frontal and occipital lobes.

It contains the postcentral gyrus (primary sensory cortex) and is mainly responsible for sensory perception. The parieto-occipital sulcus separates it from the occipital lobe.

Temporal lobe (mainly responsible for?)

Primarily responsible for hearing, language comprehension, and memory. Lies inferior to the lateral fissure. It contains the primary auditory cortex (hearing). It sits in the middle cranial fossa.

Occipital lobe (mainly responsible for?)

Most posterior lobe, behind the parieto-occipital sulcus. It contains the primary visual cortex (vision).

Lateral Fissure

Deep groove on the side of the brain that separates the temporal lobe from the frontal and parietal lobes.

Longitudinal fissure

A deep midline groove that separates the left and right cerebral hemispheres. It is seen from the superior view.

Transverse fissure

Deep groove separating the cerebrum (occipital lobes) from the cerebellum below it.

Central sulcus

Groove that separates the frontal lobe (in front) from the parietal lobe (behind). It lies between the precentral and postcentral gyri.

Parieto-occipital sulcus

Groove seen on the medial view that separates the parietal lobe from the occipital lobe.

Precentral gyrus (contains?)

Gyrus of the frontal lobe, just in front of the central sulcus. It contains the primary motor cortex (initiates voluntary movement). "Pre" means before the central sulcus.

Postcentral gyrus (contains?)

Gyrus of the parietal lobe, just behind the central sulcus. It contains the primary sensory cortex (receives and perceives sensory information). "Post" means after the central sulcus.

Anterior Cranial Fossa (which lobe?)

The most anterior and highest "step" of the skull floor. It holds the frontal lobes.

Middle Cranial Fossa (which lobe?)

The middle step of the skull floor, on both sides of the midline. It holds the temporal lobes.

Posterior Cranial Fossa (which lobe?)

The most posterior step of the skull floor. It holds the cerebellum.

Cortex (3 main areas?)

The outer layer of gray matter of the cerebrum, folded into gyri and sulci.

Functions: conscious thought, speech, memory, evaluating sensory input, personality, and initiating voluntary movement.

It has three functional areas:

- motor areas (initiate movement)

- sensory areas (receive sensory information and perception),

- association areas (complex integration).

Prefrontal cortex (Function&location?)

Anterior frontal lobe. Function: personality and character traits.

Primary motor cortex (Function&location?)

Located in the precentral gyrus (frontal lobe). Function: initiates movement and fine motor control.

Broca's motor speech area (Function&location?)

Located in the frontal lobe, in the dominant hemisphere only. Function: motor speech (producing speech).

Primary sensory cortex (Function&location?)

Located in the postcentral gyrus (parietal lobe). Function: sensory reception and perception.

Primary auditory cortex (Function&location?)

Located in the temporal lobe. Function: hearing.

Primary visual cortex (Function&location?)

Located in the occipital lobe. Function: vision.

Extra: The motor and sensory homunculi are "little man" maps of the body across the precentral and postcentral gyri. Body parts needing fine control or sensitivity (hands, lips, tongue) take up more cortex.

White matter (three fiber types?)

Internal region of the cerebrum made of myelinated axons. It connects gray matter areas and coordinates communication. It has three fiber types

1. Commissural fibers

2. Association fibers

3. Projection fibers

Commissural fibers

Connects gray matter areas between the two hemispheres (left ↔ right).

Example: corpus callosum.

Corpus callosum

Large arch of commissural fibers at the base of the longitudinal fissure, above the lateral ventricles. It is the main bridge between the hemispheres

Association fibers

Connect parts of the same hemisphere. Example: general cerebral white matter.

Projection fibers

Connect the cerebral cortex to other parts of the CNS (cerebrum → brainstem/spinal cord). Examples: corona radiata, internal capsule, spinal tracts.

Basal nuclei (ganglia) (function? Consists of?)

Collections of nerve cell bodies (inner gray matter) deep in the cerebrum.

Function: primarily responsible for regulating movement by controlling its initiation and termination and inhibiting muscle contractions.

Damage can cause muscle rigidity and resting tremors, as seen in Parkinson's and Huntington's diseases.

Consists of the caudate nucleus, putamen, and globus pallidus.

Caudate nucleus

Basal nucleus with a C-shape "tail" that arches over the thalamus, next to the lateral ventricle.

Putamen

Basal nucleus on the lateral side of the group. In the lateral view, the putamen is the outermost and the globus pallidus is medial to it.

Globus pallidus

Basal nucleus medial to the putamen. It sits within and next to the putamen.

Thalamus (function?)

Paired central brain structure that encloses the third ventricle.

It is the major relay center for all sensation entering the cerebral cortex EXCEPT olfaction (smell). It also aids in motor activity.

Hypothalamus (function?)

Paired central brain structure below the thalamus.

It is the major regulator of the body's internal environment (homeostasis) through the autonomic, limbic, and endocrine systems. It is near the optic chiasm and pituitary gland.

Epithalamus (function?)

Paired central brain structures located superior and posterior to the thalamus, forming the roof of the third ventricle.

It helps regulate the sleep-wake cycle with the hypothalamus.

Pineal body/gland

The main projection of the epithalamus. It secretes the hormone melatonin.

Brain Stem (Consists of? Function? Nerves?)

Made of the midbrain, pons, and medulla oblongata (superior to inferior).

Functions: Controls vital automatic functions (heart rate and breathing) and relays nerve signals between the brain and spinal cord.

Nuclei for cranial nerves III-XII are in the brain stem.

Midbrain (Functions? Components? Nerves?)

Most superior part of the brainstem. Contains the cerebral peduncles (ventral surface), superior colliculi (dorsal surface), and inferior colliculi (dorsal surface)

Controls visual and auditory reflexes, eye movements, and motor control.

Contains the oculomotor (III) and trochlear (IV) cranial nerve nuclei, as well as the cerebral peduncles and structures involved in visual and auditory processing.

Cerebral peduncles (Function?)

Ventral bulges of the midbrain that carry descending motor fibers

Carry descending motor signals from the cerebrum through the midbrain to the brainstem and spinal cord for voluntary movement.

Superior colliculi (Function?)

Paired dorsal bulges of the midbrain.

Controls visual reflexes and direct eye and head movements toward visual stimuli.

Inferior colliculi (Function?)

Paired dorsal bulges of the midbrain inferior to the superior colliculi.

Primarily responsible for auditory reflexes and processing sound information.

Substantia nigra

Dark pigmented nucleus in the midbrain. It is degenerated in Parkinson's disease.

Pons (Function? Nervses?)

The bulge between the midbrain and medulla, ventral to the cerebellum.

Relays signals through ascending and descending tracts between higher brain centers and the spinal cord and between the motor cortex and cerebellum.

Cranial nerve nuclei: trigeminal (V), abducens (VI), facial (VII), vestibulocochlear (VIII).

Medulla Oblongata (Nerves?Contains?)

Most inferior part of the brain stem, continuous with the spinal cord. Contains Pyramids.

Controls vital autonomic reflex functions, including heart rate, blood pressure, and breathing, and houses visceral motor nuclei for autonomic reflexes.

Cranial nerve nuclei: vestibulocochlear (VIII), glossopharyngeal (IX), vagus (X), part of accessory (XI), hypoglossal (XII).

Pyramids (Function?)

Ventral bulges contain descending motor tracts that carry voluntary movement signals.

Most fibers cross in the lower medulla, so each brain hemisphere controls the opposite side of the body.

Cerebellum (Function? Components?)

Located in the posterior cranial fossa, posterior to the brain stem and inferior to the occipital lobes, separated from them by the transverse fissure.

Function: Coordinates the timing and patterns of muscle contractions for smooth movements and corrects movement errors.

Anatomical Parts:

1) Cerebellar Hemispheres

3) Arbor Vitae (white matter)

3) Folia (gyri)

Cerebellar hemispheres

The two lateral halves of the cerebellum, seen best from the inferior view.

Arbor vitae (Function?)

The white matter of the cerebellum, with a branching tree pattern in a midsagittal view.

Carries nerve signals to and from the cerebellar cortex to coordinate movement and balance.

Folia (Function?)

Thin, leaf-like folds (gyri) of gray matter on the cerebellar surface that increase surface area for processing information involved in coordinating movement, balance, and posture.