Nervous System Part 2 (PDF)

Nervous System Dr. Luann Cullen EARLY EMBRYONIC DEVELOPMENT OF THE NERVOUS SYSTEM The neuroectoderm begins to fold inward to form the neural groove. As the two sides of the neural groove converge, they form the neural tube, which lies beneath the ectoderm. The anterior end of the neural tube wil...

Nervous System Dr. Luann Cullen EARLY EMBRYONIC DEVELOPMENT OF THE NERVOUS SYSTEM The neuroectoderm begins to fold inward to form the neural groove. As the two sides of the neural groove converge, they form the neural tube, which lies beneath the ectoderm. The anterior end of the neural tube will develop into the brain, and the posterior portion will become the spinal cord. The neural crest develops into peripheral structures. Neurulation video neurulation_animation.mp4 Early embryonic development SPINAL BIFIDA (a) Spina bifida is a birth defect of the spinal cord caused when the neural tube does not completely close during embryonic development. The result is the emergence of meninges and neural tissue through the vertebral column. (b) Spinal bifida is evident in this ultrasound taken at 21 weeks. PRIMARY AND SECONDARY VESICLE STAGES OF DEVELOPMENT The embryonic brain develops complexity through enlargements of the neural tube called vesicles; (a) The primary vesicle stage has three regions, and (b) the secondary vesicle stage has five regions. The neural tube develops into 3 primary vesicles Forebrain Midbrain Hindbrain As development proceeds the tube is further divided into 5 secondary vesicles. Forebrain Midbrain = Mesencephalon Hindbrain The fully developed brain grows from the five secondary vesicles BLOOD SUPPLY TO THE BRAIN The blood supply to the brain enters through the internal carotid arteries and the vertebral arteries. Blood Supply and the Blood Brain Barrier System THE BLOOD BRAIN BARRIER The BBB controls movement of substances between the blood and brain tissues The brain is surrounded by connective tissues called the meninges MENINGEAL LAYERS OF THE SUPERIOR SAGITTAL SINUS The layers of the meninges in the longitudinal fissure of the superior sagittal sinus are shown, with the dura mater adjacent to the inner surface of the cranium, the pia mater adjacent to the surface of the brain, and the arachnoid and subarachnoid space between them. An arachnoid villus is shown emerging into the dural sinus to allow CSF to filter back into the blood for drainage. DURAL SINUSES AND VEINS Blood drains from the brain through a series of sinuses that connect to the jugular veins. The ventricles of the brain are fluid filled chambers Lateral ventricles Interventricular foramen 3rd ventricle Cerebral aqueduct 4th ventricle Central canal Cerebral spinal fluid (CSF) fills the ventricles CEREBROSPINAL FLUID CIRCULATION CSF is made in the choroid plexus, cellular structures found in the four ventricles, and is circulated through the ventricular system and then enters the subarachnoid space around the brain. CSF is reabsorbed into the blood at the arachnoid granulations, where the arachnoid membrane emerges into the dural sinuses. The Flow of Cerebrospinal Fluid  Major Regions of the Brain Cerebrum (83% vol.) (forebrain) Diencephalon Thalamus Hypothalamus Brainstem Midbrain Cerebellum Pons (10% vol.) Medulla oblongata Major brain regions and functions Cerebrum: cerebral cortex - higher brain functions, sensory and motor cortex. Cerebellum: coordination of voluntary movement, balance, posture, muscle tone. Diencephalon: Contains the thalamus and hypothalamus, information relay center, primitive functions, pituitary control THE CEREBRUM (CEREBRAL CORTEX) The cerebrum is the largest component of the CNS in humans, and the most obvious aspect of it is the folded surface called the cerebral cortex.  THE DIENCEPHALON The diencephalon is composed primarily of the thalamus and hypothalamus, which together define the walls of the third ventricle. The thalami are two elongated, ovoid structures on either side of the midline that make contact in the middle. The hypothalamus is inferior and anterior to the thalamus, culminating in a sharp angle to which the pituitary gland is attached. THE BRAIN STEM The brain stem comprises three regions: the midbrain, the pons, and the medulla. The brainstem contains vegetative centers for control of cardiovascular, respiratory, digestive, and other function. Midbrain: The mesencephalon sits at the top of the brainstem and connects to the cerebrum. It does primitive sensory-motor processing of info to and from cortex, vision, hearing, eye movements, body movement. Pons: Contains relay centers, control of arousal, respiration. Medulla: heart rate and breathing centers LOBES OF THE CEREBRAL CORTEX The cerebral cortex is divided into four lobes. Extensive folding increases the surface area available for cells to occupy and generate cerebral functions. Each area of the cerebral cortex has a specialized function. The cerebral hemispheres are divided into 4 lobes Frontal lobe Parietal lobe Temporal lobe Occipital lobe The cerebral hemispheres contain a number of deep grooves called sulci Central sulcus Parieto-occipital sulcus Parietal lobe Frontal lobe Occipital lobe Temporal lobe Lateral sulcus Between the sulci are raised surfaces of the cerebral cortex called gyri precentral postcentral gyrus gyrus Parietal lobe Frontal lobe Occipital lobe Temporal lobe Superior View of the Brain Inferior View of the Brain Lateral View of the Brain Medial Section of the Brain THE CEREBELLUM IS FOR MOTOR COORDINATION The cerebellum is situated on the posterior surface of the brain stem. Descending motor intput from the brain enters the cerebellum through the white matter of the pons. Ascending input from the periphery and spinal cord enters through the fibers of the inferior olive. Output goes to the midbrain, which sends a descending signal to the spinal cord. The limbic system is involved in learning and memory, emotional processing, and other primitive functions  THE BASAL NUCLEI ARE FOR PRIMITIVE MOTOR, COGNITIVE AND EMOTIONAL PROCESSING The major components of the basal nuclei, shown in a frontal section of the brain, are the caudate (just lateral to the lateral ventricle), the putamen (inferior to the caudate and separated by the large white-matter structure called the internal capsule), and the globus pallidus (medial to the putamen). The basal ganglia  CONNECTIONS OF BASAL NUCLEI Input to the basal nuclei is from the cerebral cortex, by excitatory synapses releasing glutamate as the neurotransmitter. This input is to the striatum, or the caudate and putamen. The outputs of the striatum project to the internal segment of the globus pallidus and the substantia nigra pars reticulata (GPi/SNr). This is an inhibitory pathway, in which GABA is released at the synapse. Target cells are therefore hyperpolarized and less likely to fire. Other nuclei in the basal circuit are involved in processing information in the basal ganlia. The final output from the basal nuclei is to the thalamus in an inhibitory projection using GABA, and the thalamus reports back to the cortex to achieve the final functions of the basal ganglia. PARKINSONS DISEASE IS CAUSED WHEN DOPAMINERGIC NEURONS IN THE SUBSTANTIA NIAGRA UNEXPECTEDLY DIE Communication between the different nuclei in the basal nuclei is disrupted and motor control deteriorates. QUESTIONS