Human Anatomy: The Nervous System Lecture PDF

BIOL2002SEF HUMAN ANATOMY THE NERVOUS SYSTEM Dr CHEUNG Ka Tik 1 September 23, 2024  OVERVIEW OF THE NERVOUS SYSTEM  The nervous system has two major anatomical subdivisions;  The central nervous system (CNS)  The peripheral ne...

BIOL2002SEF HUMAN ANATOMY THE NERVOUS SYSTEM Dr CHEUNG Ka Tik 1 September 23, 2024  OVERVIEW OF THE NERVOUS SYSTEM  The nervous system has two major anatomical subdivisions;  The central nervous system (CNS)  The peripheral nervous system (PNS) 2  SUBDIVISION OF THE NERVOUS SYSTEM 3 4 CELLS OF THE NERVOUS SYSTEM There are two cells of the nervous system. These are; ✓Neuron ✓Neuroglia The functional unit of the nervous system is the neuron or nerve cell Neuroglia or glial are supportive cells in the nervous system that aid the function 5 of neurons NEURONS (Nerve Cells) Neurons have three fundamental physiological properties: 1. Excitability 2. Conductivity 3. Secretion A typical neuron is divided into three parts; ✓ Soma or cell body (perikaryon) ✓ Dendrites ✓ Axon 6 STRUCTURE OF A NEURON 7  CLASSIFICATION OF NEURONS Neurons may be classified according to structure or function. Function Structure Sensory (afferent) Unipolar neurons neuron Bipolar neurons Interneuron Multipolar (association) neurons Motor neuron Anaxonic neurons 8 9 FUNCTIONAL CLASSIFICATION 10 STRUCTURAL CLASSIFICATION 11 NEUROGLIA (Glia) There are six types of supportive cells Four occur in the CNS ✓ Oligodendrocytes ✓ Ependymal cells ✓ Microglia ✓ Astrocytes Two occur in the PNS ✓ Schwann cells (Neurilemmocytes) ✓ Satellite cells 12 13  TYPES OF NEUROGLIA 14  SYNAPTIC TRANSMISSION The meeting point between a neuron and any other cell is called a synapse The synapses b/t neurons and skeletal muscle cells are referred to as myoneural or neuromuscular junction Synapse can be; ✓Chemical synapse ✓Electrical synapse 15  ANATOMY OF A SYNAPSE 16  CENTRAL NERVOUS SYSTEM The CNS consists of the brain and spinal cord CNS protected by a cranium surrounding the brain Vertebral column surrounding the spinal cord The CNS is bathed in cerebrospinal fluid The CNS is composed of gray and 17 white matter  THE BRAIN  The brain is semi-spherical but soft delicate complex organ.  It is the center for control and integration  An adult brain weighs near 1.5 kg (3-3.5lbs)  The brain makes up 2% of a human's body mass  Composed of an estimated 100 billion (1011) neurons  Anatomically, the brain is divided into 3 regions;  Forebrain  Midbrain 18  Hindbrain  DIVISIONS OF THE BRAIN 19 20 The brain is lined by membrane called meninges.  The brain is conspicuously marked by surface gyri (folds) and sulci (grooves). The human brain is composed of neurons, glial cells and blood vessels. It also consists of four internal, interconnected chambers called ventricles. 21  MENINGES OF THE CENTRAL NERVOUS SYSTEM The CNS is protected by three connective tissue membranes coverings called meninges From superficial to deep, they are; Dura mater, Arachnoid mater, Pia 22 mater  CEREBROSPINAL FLUID & VENTRICLES OF THE BRAIN The brain has four internal chamber called ventricles ✓Two lateral ventricles ✓A third and fourth ventricles The fourth ventricle is located in the brain stem The cerebral aqueduct (aqueduct of Sylvius) passes through the midbrain to link the third and fourth ventricles.  CSF is a clear fluid that forms a protective 23cushion around and within the CNS VENTRICLES OF THE BRAIN 24 25 SURFACE ANATOMY OF THE BRAIN 26  FOREBRAIN  Forebrain consist of the following regions; Telecephalon (cerebrum) and Diencephalon (Thalamus, hypothalamus, epithalamus and pituitary gland) ❖ CEREBRUM  The cerebrum is the largest part of the brain.  It is divided into two hemispheres separated by the longitudinal fissure.  The hemispheres are prominently marked with gyri and sulci.  Portions of the two hemispheres are connected internally by the corpus callosum  Each cerebral hemisphere is subdivided by deep sulci, or fissures, into the five lobes: Frontal, Parietal, Occipital, Temporal 27 and Insula LOBES OF THE CEREBRUM 28 29 ANATOMY OF THE CEREBRUM 30 DIENCEPHALON  A major autonomic region of the brain that consists of vital structures such as;  Thalamus, Hypothalamus , Epithalamus , Pituitary gland  These structures surround the third ventricle of the brain  The thalamus is a large ovoid mass of gray matter  The hypothalamus is a small portion of the diencephalon inferior to the thalamus  The epithalamus is the dorsal portion of the diencephalon that includes a thin roof over the third ventricle.  The pituitary gland, or hypophysis, is positioned on 31 the inferior aspect of the diencephalon  ANATOMY OF THE DIENCEPHALON 32  MIDBRAIN The midbrain is a short section of the brain stem between the diencephalon and the pons (Hindbrain) A short segment of the brainstem that connects the hindbrain and forebrain Within the midbrain is the cerebral aqueduct It includes important centers for vision, hearing, pain, and motor 33control  ANATOMY OF THE MIDBRAIN 34  HINDBRAIN  The embryonic hindbrain differentiates into two subdivisions the metencephalon and myelencephalon  The metencephalon is the most superior portion of the hindbrain.  The pons which measures about 2.5 cm long, forms a broad anterior bulge in the brainstem just rostral to the medulla.  It conducts signals up and down the brainstem and between the brainstem and cerebellum  The cerebellum is the largest part of the hindbrain and receives most of its input by way of the pons. 35Occupies the inferior and posterior aspect of the cranial cavity ANATOMY OF HINDBRAIN 36  MYELENCEPHALON Myelencephalon contain the medulla oblongata The medulla oblongata is a bulbous structure about 3 cm (1In) long Externally, the medulla resembles the spinal cord 37  SPINAL CORD  It is an elongated cylindrical structure that is a ropelike bundle of nervous tissue  In adults, it averages about 1.8 cm thick and 45 cm long  It begins as a continuation of the medulla oblongata at the level of the foramen magnum  The spinal cord serves three principal functions: Conduction, Locomotion and Reflexes  The cord gives rise to 31 pairs of spinal nerves. the part supplied by each pair of spinal nerves is called a segment.  The spinal cord is divided into cervical, thoracic, lumbar, and sacral regions. 38 STRUCTURE OF THE SPINAL CORD (Surface Anatomy) 39  CROSS-SECTIONAL ANATOMY  The spinal cord consists of two kinds of nervous tissue called gray and white matter.  Gray matter has a relatively dull color because it contains little myelin.  It has butterfly- or H-shaped in cross sections  It contains the somas, dendrites, and proximal parts of the axons of neurons.  It is the site of synaptic contact between 40neurons (information processing)  CROSS- SECTION AL SPINAL CORD 41 White matter contains an abundance of myelinated axons, which give it a bright, pearly white appearance. It is composed of bundles of axons called tracts or fascicule It carry signals from one part of the CNS to another. The spinal cord has two tracts; Ascending and descending tract Ascending tracts carry sensory information up the cord and descending tracts conduct motor impulses down 42 TRACT OF THE SPINAL CORD 43  Types of neuron Neurons are classified into 3 main groups Sensory neurons, motor neurons and interneurons. 44  Sensory, Motor and interneuron 45  Motor neuron (efferent neuron) carry impulses to the effectors (muscles and glands). Motor neuron linked to skeletal muscles are called somatic neuron. Motor neurons linked to smooth muscle, cardiac muscle and glands are called visceral. 46 PERIPHERAL NERVOUS SYSTEM The (PNS) is that portion of the nervous system outside the central nervous system Sensory receptors within the sensory organs, neurons, nerve, ganglia, and plexuses are all part of the PNS The nerves of the PNS are classified as; cranial nerves or spinal nerves, 47  GENERAL ANATOMY OF NERVES AND GANGLIA A nerve is a cordlike organ composed of numerous nerve fibers (axons) bound together by connective tissue. Nerve fibers of the peripheral nervous system are ensheathed in Schwann cells, which form a neurilemma and often a myelin sheath around the axon. Nerves has:  endoneurium, perineurium and epineurium 48  ANATOMY OF A NERVE 49  Types of neuron Neurons are classified into 3 main groups Sensory neurons, motor neurons and interneurons. 50  Motor neuron (efferent neuron) carry impulses to the effectors (muscles and glands). Motor neuron linked to skeletal muscles are called somatic neuron. Motor neurons linked to smooth muscle, cardiac muscle and glands are called visceral. 51 Sensory neurons carry impulses from receptors to the central nervous system (afferent neurons) Sensory and motor neurons make up the peripheral nervous system. Interneurons are found entirely within the central nervous system. They are arranged so as to carry only sensory and motor impulses or to integrate these functions. Some interneurons in the brain are concerned with thinking, learning and memory. 52  Nerve impulses are action potential which carry information along the neuron membrane. Neurons not carrying an impulse has abundant Na+ ions outside the cell and abundant K+ and negatively charged ions inside. 53  Sensory, Motor and interneuron 54  CRANIAL NERVES Cranial nerves are nerves that emerge directly from the brain and the brainstem. There are 12 pairs of cranial nerves, numbered I to XII They relay information between the brain and parts of the body.  Considers to be parts of both CNS and PNS They are traditionally classified as sensory, 55 motor or mixed base on their functions.  CRANIAL NERVES 56 57  SPINAL NERVES  There are 31 pairs of spinal nerves: 8 cervical (C1–C8), 12 thoracic (T1–T12), 5 lumbar (L1–L5), 5 sacral (S1–S5), and 1 coccygeal (Co).  The first cervical nerve emerges between the skull and atlas  The others emerge through intervertebral foramina, including the anterior and posterior foramina of the sacrum and the sacral hiatus. 58 59  Major Peripheral nerves Nerve Spinal nerves that Distribution contribute Phrenic C3 – C5 Diaphragm Radial C5 – C8, T1 Skin and muscles of posterior arm, forearm, and hand, thumb and first 2 fingers Median C5 – C8, T1 Skin and muscles of anterior arm, forearm and hand Ulnar C8, T1 Skin and muscles of medial arm, forearm and hand; little finger and ring finger Intercostal T2 – T12 Intercostal Muscles, abdominal muscles, skin of trunk Femoral L2- L4 Skin and muscles of anterior thigh, medial leg and foot Sciatic 60 L4 – S3 Skin and muscles of posterior thigh, leg and foot  AUTONOMIC NERVOUS SYSTEM (ANS)  ANS is motor nervous system that controls glands, cardiac muscle, and smooth muscle  The primary target organs of the ANS are the viscera of the thoracic and abdominal cavities  Its job is to regulate such fundamental states and life processes as heart rate, blood pressure, body temperature, respiratory airflow, pupillary diameter, digestion, energy metabolism, defecation, and 61 urination.  DIVISION OF THE ANS  The ANS has two subsystems  Sympathetic  parasympathetic divisions  Sympathetic (Thoracolumbar) Division The sympathetic division is also called the thoracolumbar division  It has relatively short preganglionic and long postganglionic fibers 62 PARASYMPATHETIC DIVISION The parasympathetic division is also called the craniosacral Somas of the preganglionic neurons are located in the pons, medulla oblongata, and segments S2 to S4 of the spinal cord The parasympathetic division has long preganglionic fibers reaching almost all the way to the target cells short postganglionic fibers that cover the rest of the distance. 63  Thanks For Your Attention QUESTIONS!! COMMENTS!! CONTRIBUTIONS!!! 64