BIOM 3200 Unit 10: Nervous System

Brain Development

14 days after conception the embryo splits into 3 germ layers: 1) ectoderm 2) endoderm 3) mesoderm 20 days after conception the ectoderm forms a groove that becomes the neural tube (a channel that develops into the brain and spinal cord) 4 weeks after conception the brain begins to organize into 3 distinct swellings in the neural tube: 1) prosencephalon (further develops into telencephalon & diencephalon) 2) mesencephalon 3) rhombencepalon (further develops into myelencephalon & metencephalon)

Composition of Vertebral Column

7 cervical vertebrae 12 thoracic vertebrae 5 lumbar vertebrae the sacrum the coccyx

Spinal Nerve Breakdown

8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal

Plexus

A combination or network of nerves that supply a specific region of the body. Ex. the brachial plexus is comprised of 4 cervical nerves and 1 cranial nerve, and it supplies the chest, shoulder, arm, forearm, and hand.

Spinal Cord

A continuation of the medulla caudally as it leaves the skull through an opening called the magnum foramen.

Ventricles

Adult brain contains fluid-filled chambers called ventricles that are filled with cerebrospinal fluid.

Afferent vs Efferent Nerves

Afferent (sensory) nerves that enter the spinal cord branch into the dorsal root. Efferent (motor) nerves that leave the spinal cord leave by the ventral root.

Behaviours/Emotions Associated With the Limbic System

Aggression, fear, feeding patterns, sex drives, and reward and punishment systems.

Reflex

An involuntary response to a stimulus.

Pons

Anterior to the cerebellum. Bridges descending pathways from the cerebral cortex to the cerebellar cortex and medulla with ascending pathways travelling through the medulla to the thalamus cranially. It regulates respiration depth and frequency.

Spinal Nerves

Arise directly from the spinal cord and are also comprised of a mix of sensory and motor neurons, and voluntary and involuntary functions. There are 31 pairs of spinal nerves. They are labelled by the level of vertebrae where they arise and are numbered from cranial to caudal.

Ascending vs Descending Tracts of Spinal Cord

Ascending tracts convey sensory information from the body to the brain. - Spinocerebellar tract conveys sensory, proprioceptive information to the cerebellum. - Spinothalamic tract conveys pain and temperature to the thalamus. Descending tracts transmit efferent information from the brain to target tissues. - Corticospinal tract conveys voluntary somatic motor information from the motor cortex to spine. - Extrapyramidal tracts connect the reticular formation and vestibular apparatus of the ear to lower motor neurons and provide involuntary motor control.

Ascending vs Descending Tracts

Ascending tracts of nerves convey sensory information from the periphery to the brain. Descending tracts of nerves send motor nerve impulses from the brain down the spinal cord.

Temporal Lobe Functions

Auditory sensation; memory of auditory and visual experiences.

Adrenergic Stimulation

Causes both excitation and inhibition depending on tissue. All adrenergic receptors act via G-proteins.

Central Nervous System (CNS)

Composed of brain and spinal cord.

Rhombencephalon (Hindbrain)

Composed of the metencephalon superiorly (top) and the myelencephalon inferiorly (bottom).

Myelencephalon

Comprises the medulla oblongata.

Metencephalon

Comprises the pons and cerebellum.

Menginges

Connective tissue layers that encase the brain and spinal cord.

Reticular Formation

Connects carious areas of the brain together and processes a great deal of neuronal information. An ascending tract of the reticular formation determines consciousness and is termed the reticular activity system (RAS).

Peripheral Nervous System (PNS)

Consists of nerves that connect the CNS to all sensory receptors and effectors of the body. They are axons grouped into bundles called nerves. Peripheral nerves are myelinated by Schwann cells.

Diencephalon

Consists of the thalamus and hypothalamus.

Limbic System

Consists of various brain regions responsible for emotion, behaviour, motivation, smell, and long term memory. Includes areas of the cerebrum (cingulate gyrus, amygdala, hippocampus, septal nuclei, anterior insult) as well as the thalamus and hypothalamus. There are no connections between the limbic system and cerebral cortex, which may explain why humans have no control over their emotions.

Medulla Oblongata

Contains vital centres which are important for autonomic control of the heart and peripheral blood vessels, respiratory rate and depth, and sneezing, coughing, swelling, and vomiting reflexes. It contains a diffuse neuronal network system called the reticular formation.

Parietal Lobe Functions

Cutaneous and muscular sensations; speech; texture and shapes.

Longitudinal Fissure

Deep groove that divides the cerebrum into right and left hemispheres.

Central Sulcus

Divides the cerebrum into anterior and posterior (front and back) and separates the frontal and parietal lobes.

Mesencephalon (Midbrain)

Forms the upper part of the brain stem, and connects the pons and cerebellum with diencephalon. Includes: - Corpora Quadrigemina (visual auditory reflexes) - Cerebral Peduncles (ascending/descending tracts) - Red Nucleus (motor coordination) - Substantia Nigra (motor circuit)

Autonomic Motor Nerves

Innervate organs whose functions are NOT usually under voluntary control.

Occipital Lobe Functions

Integration of movements in focusing eyes; correlation of visual images with previous experiences; conscious perception of vision.

Autonomic Motor Control

Involves two neurons in the efferent pathway; the first of these neurons has its cell body in the gray matter of the brain or spinal cord. Preganglionic neuron in the grey matter synapses with the postganlionic neuron within the autonomic ganglion, which is a collection of cell bodies outside the CNS.

Basal Nuclei

Islands of grey matter buried within the white matter. They are critical for proper body movements.

Sympathetic Nervous System

It is also called the thoracolumbar division of the autonomic system because its preganglionic fibers exit the spinal cord from the first thoracic (Tl) to the second lumbar (L2) levels.

Cerebrum

Largest part of the brain and the location where higher brain functions arise. The surface of the cerebrum is grey matter, and consists mostly of neuronal cell bodies. White matter is found deep in the cerebrum and consists mostly of myelinated axons that connects grey matter with other areas of the brain.

Cerebellum

Located posteriorly and consists of an outer grey matter layer and an inner white matter layer. It received input from proprioceptors in joins, tendons, and muscles, and is therefore involved in motor activities. Balance sensory information from the vestibular apparatus of the ear is received which allows the cerebellum to maintain balance. It is also responsible for coordinating learned complex movements such as riding a bicycle.

Hypothalamus

Master controller of lower autonomic functions, including the autonomic nervous system and endocrine system. It is also the body's thermostat. It contains hunger and thirst centres, and contributes to emotion and behaviour.

Insula Lobe Function

Memory; pain and visceral integration.

Types of Cholinergic Receptors

Nicotinic receptors: - Nicotine and acetylcholine stimulate these receptors located in the neuromuscular junction of skeletal muscle fibers and in the autonomic ganglia. - Always excitatory. Muscarinic receptors: - Muscarine and acetylcholine stimulates these receptors in the visceral organs. - Can be excitatory or inhibitory.

12 Cranial Nerves

Olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal. "On Old Oklahoma's Towering Top A Fine Vet Gladly Viewed Some Horses"

Precentral Gyrus

Part of the frontal lobe adjacent to the central sulcus.

Postcentral Gyrus

Part of the parietal lobe adjacent to the central sulcus; involved in somatic sensation from receptors all over the body.

Collateral Ganglia

Postganglionic fibers that arise from the collateral ganglia innervate organs of the digestive, urinary, and reproductive systems.

Cerebrospinal Fluid (CSF)

Provides nourishment and protection. Produced by specialized tissue that lines the ventricles called choroid plexuses.

Lateral Sulcus

Separates temporal lobe from parietal and frontal lobes.

Alpha vs Beta Adrenergic Receptors

Stimulation of α1 adrenergic receptors consistently causes contraction of smooth muscles. Stimulation of beta-adrenergic receptors promotes the relaxation of smooth muscles but increases the force of contraction of cardiac muscle and promotes an increase in heart rate.

Sympathetic vs Parasympathetic Nervous System

Sympathetic: fight or flight Parasympathetic: rest and digest

Where Does the Spinal Cord Terminate?

Terminates at the 2nd lumbar vertebrae, called the conus medullaris. This is due to differences in growth rate between the spinal cord and the vertebral column.

4 Ventricles of the Brain

The 2 lateral ventricles are found deep in the cerebral hemispheres and join the third ventricle at the level of the diencephalon. The third ventricle is found in the diencephalon between the left and right thalamus. The fourth ventricle is located at the level of the pons, cerebellum, and medulla.

Thalamus

The brain's sensory control center, located on top of the brainstem. It directs messages to the sensory receiving areas in the cortex and transmits replies to the cerebellum and medulla.

Parasympathetic Nervous System

The parasympathetic division is also known as the craniosacral division of the autonomic system because its preganglionic fibers originate in the brain (specifically, in the midbrain, medulla oblongata, and pons) and in the second through fourth sacral levels of the spinal column.

Flexor Reflex

The quick contraction of flexor muscles resulting in the withdrawal of a limb from an injurious stimulus. This reflex is polysynaptic due to the presence of an interneuron.

Knee-Jerk Reflex

The reflex elicited when you strike the patellar tendon below the knee.

Subarachnoid Space

The space between the pia mater and arachnoid mater that is filled with CSF. The purpose of this space is to provide a buoyant layer that protects the brain from damage. The CSF in this space drains through specialized areas of the meninges called arachnoid villi.

Ventricles are Joined by Foramen

This facilitates flow of CSF in and out of the brain. Lateral ventricles connect to the third ventricle via the interventricular foramen. The third ventricle connects to the fourth ventricle via the mesencephalic aqueduct. The fourth ventricle connects to the subarachnoid space via the median aperture.

Frontal Lobe Functions

Voluntary motor control of skeletal muscles; personality; higher intellectual processes (concentration and decision making); verbal communication.

White and Grey Matter in Spinal Cord

White outer layer and grey inner layer, which is OPPOSITE to the cerebrum.

Minimum Components of Reflex Arc

1) A sensory receptor to detect stimulus. 2) A sensory neuron to transmit to spinal cord. 3) A motor neuron to transmit involuntary impulses to an effector. 4) An effector organ which will bring about a response. This would be called monosynaptic.

Effectors for Autonomic Neurons

1) Cardiac muscle 2) Smooth muscle 3) Glands

3 Layers of the Meninges

1) Dura mater is the outermost tough layer. 2) Arachnoid mater is the delicate middle layer. 3) Pia mater is the delicate innermost layer.

What Protects the Spinal Cord From Damage?

1) Vertebral column 2) Meninges 3) CSF