lecture 6

The Nervous System

• Under control of the Nervous System is every function of the human body
• The functions of the nervous system include detecting stimuli in the environment before recognizing how important external stimuli are
• Nervous sustem also helps making decisions based on how significant something is and executing a response

Major Divisions

• The Peripheral Nervous System (PNS) aims to detect environmental stimuli and transmit information to the CNS (Central Nervous System)
• The PNS carries out orders that CNS gives
• The CNS's function is to receive and analyze incoming information
• The CNS also makes executive decisions and transmits decisions back to the PNS

Peripheral Nervous System

• The Somatic Nervous System is part of the peripheral nervous system
• Afferent nerves carry information from sensory neurons to the CNS
• Efferent nerves carry information from the CNS to motor neurons
• Nerves come in pairs, with one efferent/motor nerve & the other afferent/sensory nerve
• There are 31 pairs of spinal nerves
• There are 12 pairs of cranial nerves

PNS: Cranial Nerves (12 pairs)

• Olfactory (I): Sensory nerve associated with the nose
• Optic (II): Sensory nerve associated with the eye
• Oculomotor (III): Motor nerve that controls all eye muscles except those controlled by IV & VI
• Trochlear (IV): Motor nerve that controls the superior oblique muscle
• Trigeminal (V): Sensory nerve for the face, sinuses and teeth, also a motor nerve for muscles of mastication
• Abducent (VI): Motor nerve for the external rectus muscle
• Facial (VII): Motor nerve that controls muscles of the face
• Vestibulocochlear (VIII): Sensory nerve for the inner ear
• Glossopharyngeal (IX): Motor nerve for pharyngeal musculature also sensory nerve for posterior part of the tongue, tonsil and pharynx
• Vagus (X): Motor nerve for the heart, lungs, bronchi, gastrointestinal tract also it is a sensory nerve for the heart, lungs, bronchi, trachea, larynx, pharynx and gastrointestinal tract plus the external ear
• Accessory (XI): Motor nerve that controls the sternocleidomastoid and trapezius muscles
• Hypoglossal (XII): Motor nerve responsible for muscles of the tongue

PNS: Spinal Nerves (31 pairs)

• Gray matter, dorsal horn and visceral/somatic sensory nuclei are present
• Ventral and lateral horns exist
• The dorsal root ganglion exists
• Afferent nerves control sensory information
• Autonomic nerves exist for muscle control and glands via the ventral root

Autonomic Nervous System

• The cervical nerves are largely responsible for somatic motor control and sensory function within the neck, shoulders, arms, and diaphragm
• Sexual functions can include the fact tha PANS initially promotes erection (vasodilation), and followed by SANS which then controls ejaculation and vaginal contraction during orgasm (vasoconstriction)
• Timing is ensured, for everything, by SANS
• Regarding bladder function, PANS contracts to allow urination and SANS relaxes the bladder sphincter for urine storage

Components of the Reflex Arc

• Reflex arc components: receptors > afferent pathway > integrating center > efferent pathway > effector
• Pain activates thermal pain receptors in the finger
• Action potentials are generated in the afferent pathways
• Impulses move towards the spinal cord
• The spinal cord is the integrating center where the afferent neuron stimulates: excitatory interneurons stimulate motor neurons to the bicep, inhibitory interneurons inhibit motor neurons to the triceps, and interneurons are then sent to the brain
• Efferent pathways cause the biceps to contract or triceps to relax preventing excitation/traction of antagonistic muscles
• Biceps & triceps are effectors and the movement/flex of an elbow joint withdraws from the painful stimuli
• Events that occur due to the arrival of a signal in the brain via the ascending pathway are separate from the reflex arc, these include memory

Central Nervous System

• The spinal cord is located in the vertebrate spinal column
• Limited analysis and decision making occur int he spinal cord
• The spinal cord transmits information to and from the main
• The brain is in the skull
• It analyzes sensory information and creates appropriate responses

Central Nervous System: The Brain

• The brain weighs 1400 grams which is about 2% of the average body weight
• The brain's structure is folded into gyri (hills) and sulci (valleys)

Hindbrain (Rhombencephalon)

• Metencephalon can also be called the pons: sensory relay
• Cerebellum: maintains posture, timing and planning movements
• Myelencephalon can also be called the Medulla: control basic life functions like breathing, heart rate, vomiting, etc
• Medulla is located in the reticular formation which involves arousal/sleep regulations

Midbrain (Mesencephalon)

• Tectum: contains the superior colliculus which controls eye movements, and the inferior colliculus handles any auditory information
• Tegmentum: has reticular formation, substantia nigra releases dopamine and red nucleus which controls body movements

Brainstem

• The brainstem consists of the hindbrain (metencephalon & myelencephalon) and the midbrain (mesencephalon)

Diencephalon

• Thalamus as part of a central relay station:
  • Lateral Geniculate Nucleus (LGN): visual processing
  • Medial Geniculate Nucleus (MGN): auditory processing
• Hypothalamus: involved in homeostatic control
• Pituitary gland: Involved in hormonal control (master gland)
• Pineal gland: releases melatonin and is involved in sleep-wake cycle

Telencephalon I: Limbic System

• The limbic system governs emotions (anger, happiness, fear) and it is involved in storage/retrieval of memories
• This includes the Hippocampus and Amygdala

Telencephalon II: Basal Ganglia

• Basal ganglia contains widespread connection to the cortex and forebrain plus it is involved ini voluntary movements with maintenence of muscles, tone and posture
• Contains the caudate nucleus, putamen, and the globus pallidus
• Caudate nucleus and putamen are the striatum

Telencephalon III: Neocortex

• Occipital Lobe's primary function is to analyse visual information
• Parietal Lobe processes sensory information and is involved in spatial perception
• Temporal Lobe processes auditory information and language (Wernicke's area)
• Frontal Lobe controls motor programs, complex intellectual functioning, speech production (Broca's area), personality and executive function

Cortical Homunculus

• Somatosensory and motor cortices have a physical representation of the body

The Ventricular System

• Two views of ventricles, filled with cerebrospinal fluid
• Components: lateral ventricle, interventricular foramen, third ventricle, aqueduct of midbrain and fourth ventricle

The Vascular System

• Approximately 400 miles of blood vessels are in the human body
• Components of the vascular system include anterior cerebral, middle cerebral, posterior cerebral, basilar, vertebral, pontine, superior cerebellar etc