The Nervous System

Directions in the Nervous System Anterior or Rostral Posterior or Caudal Dorsal or Superior Ventral or Inferior Medial Lateral

Slice and Dice: Planes of View

Central and Peripheral Nervous Systems.

Divisions of the Nervous System CNS - Division located within the skull and spinal cord. PNS – Division located outside the skull and spine. PNS Divisions: Somatic – interacts with external environment. Composed of afferent nerves from skin, muscles, eyes, ears, etc., to the CNS and efferent nerves from the CNS that carry signals to the skeletal muscles. Autonomic – regulates internal environment. Afferent nerves carry signals from internal organs to the CNS. Efferent nerves carry signals from the CNS to internal organs. Sympathetic = autonomic motor nerves projecting from the lumbar and thoracic regions of the spine. Parasympathetic = autonomic motor nerves projecting from the brain and sacral region of the spine. Afferent – Towards the CNS. Efferent – Going away from the CNS.

The Autonomic Nervous System

The Cranial Nerves Peripheral Nerves Projecting Directly from the Brain.

Spinal Cord Gray Matter = cell bodies, unmyelinated axons. Dorsal and Ventral Horns are gray matter. White Matter = myelinated axons Spinal Nerves are attached to spinal cord at 31 different levels (62 spinal nerves).

Spinal Cord II Dorsal root axons are sensory unipolar neurons, with their cell bodies grouped just outside the spinal cord forming the dorsal root ganglion. Synaptic terminals are in dorsal horn. Ventral Root Neurons are motor (efferent) multipolar neurons with their cell bodies in the ventral horn.

The Ventricles and Cerebral Spinal Fluid Cerebral spinal fluid (CSF) is produced by the choroid plexus. Choroid plexus – networks of small vessels that protrude into the ventricle from the pia mater. Dural Sinuses – Large blood filled cavities that absorb excess CSF.

The Blood-Brain Barrier Impedes passage of many toxic substances into the brain. Caused by the tightly packed cells of the cerebral blood vessels. Astrocytes, a form of glial cell, further cover the walls of blood vessels to help maintain this dense packing. Differentially allows access of certain substances (I.e. hormones) to particular parts of the brain.

Early Brain Development

Divisions of the Adult Brain

Myelencephalon and Metencephalon Myelencephalon (also called the medulla) is composed largely of fiber tracts. The Reticular formation (little net) plays a role in arousal, attention, sleep and various cardiac, respiratory and circulatory reflexes. Metencephalon: 2 Division (1) Pons (ascending and descending fiber tracks and part of reticular formation. (2) Cerebellum (little brain) is a sensorimotor structure controlling fine motor movements.

Mesencephalon 2 Divisions: (1) Tectum or “roof” which is composed of two bumps called colliculi (little hills). There is an superior and an inferior pair of colliculi. Vision. (2) Tegmentum, ventral to the tectum, contains the RAF, fiber tracts, and the periaqueductal gray (pain and analgesia, especially opiates), the substantia nigra (sensorimotor), and the red nucleus (sensorimotor).

Diencephalon Composed of the Thalamus and the Hypothalamus. The thalamus is the top of the brainstem, and the two lobes are joined by the massa intermedia. In between the lobes is the 3 rd ventricle. Below lies the Hypothalamus, which exerts it’s effects by releasing hormones from the pituitary gland. (Pituitary actually means “snot”).

Thalamus Most Thalamic nuclei project to the cortex. Some are sensory relay nuclei such as the lateral geniculate nucleus (visual), medial geniculate nuclei (auditory) and ventral posterior nuclei (somatosensory).

Hypothalamus Below (hypo) the thalamus: Regulates release of hormones from pituitary gland. On the ventral surface is the optic chiasm where the optic nerves from the eyes come together. Most decussate or cross over to the other hemisphere of the brain here, while others remain ipsilateral. The mammilary bodiesare also on the ventral surface and involved in swallowing and olfaction.

Telencephalon: Major Fissures

Lobes of the brain

Lobes and Important Gyri

Layers of the Cortex

The Limbic System Limbic = ring (of subcortical structures). Regulation of motivated behaviors “the four F’s” Fleeing; Fighting; Feeding; and Sexual Behavior

Basal Ganglia Voluntary motor responses. Note the amygdala is considered part of both the limbic system and basal ganglia.

Types of Neurons

The Neuron

The Cell Membrane

The Neuron

Inside the Neuron

The Neuron

Myelination SchwannOligodendrocyte

Astrocytes