section 3, chapter 11

Development of the Brain & Anatomy of the Cerebrum

ivyanatomy.com

The Brain The brain has many functions.

sensations and perceptions memory reasoning decision making commands skeletal muscles regulates visceral activities provides personality

The major parts of the brain:CerebrumDiencephalonCerebellum Brainstem

Midbrain Pons Medulla oblongata

The BrainThe Brain

Figure 11.15b. Sagittal section of human brain. The major portions include the cerebrum, the diencephalon, the cerebellum, and the brainstem. The brainstem includes the midbrain, the pons, and the medulla oblongata.

Brain DevelopmentThe central nervous system develops from a neural tube that gives rise to the brain and spinal cord.

The brain begins as three primary vesicles1.prosencephalon – forebrain2.mesencephalon – midbrain3.rhombencephalon – hindbrain

The prosencephalon divides into the telencephalon & diencephalon.

The mesencephalon remains as the midbrain.

The rhombencephalon divides into the metencephalon & myelencephalon

Later the brain divides into five secondary vesicles

Five secondary vesicles: Telencephalon Diencephalon Mesencephalon Metencephalon Myelencephalon

Brain Development

Eventually the vesicles give rise to regions of the brain:

telencephalon gives rise to the cerebrum and basal nuclei

diencephalon gives rise to the thalamus, hypothalamus, and pituitary gland

mesencephalon becomes the midbrain

metencephalon forms the pons and cerebellum

myelencephalon forms the medulla oblongata.

Brain Development

functions of the cerebrum

The cerebrum provides higher brain functions:1.Interpreting senses2.Voluntary muscle movements3.Memory4.Reasoning5.Intelligence 6.Personality

Colors distinguish the lobes of the cerebral hemisphere. (a) lateral view. (b) superior view

anatomy of the cerebrum

Gyri (sing. gyrus) = Bumps or convolutions Sulci (sing. Sulcus)= Grooves in cerebrum

The cerebrum consists of a left and right hemisphere separated by a longitudinal fissure.

A bridge of nerve fibers called the cporus callosum connects the two cerebral hemispheres.

The surface of the cerebrum contains many ridges and grooves.

A transverse fissure separates the cerebrum from the cerebellum.

Lobes of the cerebrumThe cerebrum is divided into five (5) lobes bilaterally:

Frontal lobe Parietal lobe Temporal lobe Occipital lobe Insula – deep lobe

Figure 11.16(c) lateral view of the cerebrum using colors to distinguish the individual lobes. The temporal lobe is retracted to expose the

deeper insula.

The cerebral cortex is a thin outer layer of gray matter in the cerebrum.

• contains 75% of all neurons in the nervous system

Functional regions of the cerebral cortex

The cerebral medulla is a thick layer of white matter underlying the cortex.

•bulk of cerebrum•contains masses of gray matter (nuclei)

Functional regions of the cerebral cortex

Sensory Areas – cerebrum interprets impulses from receptors

Motor Areas – cerebrum controls voluntary motor actions

Association Areas - cerebrum connects from one region of the brain to another• Thoughts, emotions, and understanding

Functions of the frontal lobesFrontal LobesAssociation areas = prefrontal cortex higher intellect: judgment, complex problem solving, planning, and decision making

Motor areas = voluntary motor controlFrontal eye field – voluntary movements of eyes

Broca’s area – coordinates mouth, tongue, and pharynx for speech

• Damage may result in patient being unable to form complete sentences.

Primary motor cortex (precentral gyrus) – motor areas involved with control of voluntary muscles Pyramidal cells - cells within the frontal lobe that

initiate voluntary movements

Sensory areas of the parietal lobesPost-central gyrus (primary somatosensory cortex)– sensory areas involved with touch, temperature, pain and other cutaneous senses

Wernike’s Area – sensory speech area. Choosing words to express thoughts and emotionsUsually within left hemisphere.

Association areas General interpretive area (Wernike’s area) - integrates visual, auditory, and other sensory information an then interprets a situation.

Functions of the parietal lobes

Figure 11.18. Functional regions of the cerebral cortex. (a)motor areas that control voluntary muscles.

(b)sensory areas involved with cutaneous and other senses.

Temporal Lobes• Sensory Areas

• Hearing and smell (smell within deep temporal lobe)

•Association areas – interpret complex sensory experiences• Understand speech and reading• Stores memories of visual scenes, music, and other sensory patterns

Functions of the temporal and occipital lobes

Occipital Lobes•Visual Cortex - vision

•Visual association Combines visual images with other experiences – face recognition

Hemisphere DominanceThe left hemisphere is dominant in most individuals

The dominant hemisphere controls:• Speech, reading and writing• Analytical and computational skills

The non-dominant hemisphere controls:• Motor tasks and other non-verbal tasks•Provides emotional and intuitive thought processes

Corpus callosum enables the dominant hemisphere to control the motor cortex in the nondominant hemisphere. It also relays sensory information reaching the non-dominant hemisphere to the dominant hemisphere to be interpreted.

Basal Nuclei

The basal nuclei are three masses of grey matter deep within the cerebrum:

1. Caudate nucleus2. Putamen3. Globus pallidus

The basal nuclei secrete the inhibitory neurotransmitter dopamine• Basal nuclei interact with a region in the midbrain, called Substantia Nigra• Basal nuclei & substantia nigra facilitate voluntary movements

Parkinson’s Disease

Parkinson’s Disease (PD) results occurs from degeneration of the basal nuclei and the substantia nigra. This results in a deficiency of dopamine.

Symptoms include:• tremors at rest• poor small muscle control• rigidity• difficulties speaking

End of section 3, chapter 11

Figure 11D. Muhammad Ali has PD from many years of head injuries as a boxer. Michael J. Fox first experienced symptoms of PD at age 29,

which is unusual.