The Central Nervous System PDF

The Central Nervous System PROF. TARIG H MERGHANI Intended learning outcomes 1. List and classify different parts of the central nervous system & elucidate the basic functions of them. 2. Explain the external and internal features of different parts of the brain and spinal cord. The nervous syste...

The Central Nervous System PROF. TARIG H MERGHANI Intended learning outcomes 1. List and classify different parts of the central nervous system & elucidate the basic functions of them. 2. Explain the external and internal features of different parts of the brain and spinal cord. The nervous system Allows communication with external and internal environments.  The neuron Neurons are the basic and functional units of the nervous system. They are supported by neuroglial cells  The neuroglia Neuroglial cells are many types: ◦Microglia are phagocytic cells ◦Astrocytes support neurons, form blood brain barrier and maintain constant K+ in ECF ◦Oligodendroglial cells ◦Form myelination in CNS ◦Schwann cells ◦Form myelination in PNS  The neuron A typical neuron has cell body (or soma) and dendrites to receive information. And an axon to send nerve impulses The axons can be: ◦Myelinated (= saltatory conduction) ◦Unmyelinated (= point to point cond.)  The neuron Functional classification: ◦Sensory neuron (afferent) ◦Motor neuron (efferent) ◦Interneuron  Classification of nerve fibres Type of Diameter, Conduction General Function fiber micrometers velocity, m/sec A-alpha 13-22 70-120 alpha-motoneurons, muscle spindle primary endings, Golgi tendon organs, touch A-beta 8-13 40-70 touch, kinesthesia, muscle spindle secondary endings A- 4-8 15-40 touch, pressure, gamma-motoneurons gamma A-delta 1-4 5-25 pain, crude touch, pressure, temperature B 1-3 3-14 preganglionic autonomic C 0.1-1 0.2-2 pain, touch, pressure, temperature, 8 postganglionic autonomic 9  Other classification: Type of Diameter, Conduction General Function fiber micrometer velocity, s m/sec Ia 12-20 70-120 muscle spindle primary endings Ib 11-19 66-114 Golgi tendon organs II 5-12 20-50 touch, kinesthesia, muscle spindle secondary endings III 1-5 4-20 pain, crude touch, pressure, temperature IV 0.1-2 0.2-3 pain, touch, pressure, temperature 10 The nervous system Can be classified anatomically into: ◦Peripheral Nervous System (PNS) ◦ Cranial nerves & Spinal nerves ◦ Ganglia ◦Central Nervous System (CNS) ◦ Brain & Spinal Cord The CNS A) The Spinal cord B) The Brain  A) The Spinal cord Consists of segments Has 31 pairs of spinal nerves  A) The Spinal cord Each segment has a pair of nerve roots on each side The dorsal roots carry sensory fibers The ventral roots carry sensory fibers Unlike the brain, the white matter surrounds the grey matter The grey matter is organized into: ◦Dorsal horn ◦Ventral horn (with/ without Lateral horn) Functions of the spinal cord 1- Contains ascending and descending tracts 2- Acts as an integrating center for spinal reflexes  B) The Brain Divided into: ◦(1) Brain stem ◦(2) Diencephalon ◦(3) Cerebrum ◦(4) Cerebellum  1- The Brain Stem Between the brain and the spinal cord Consists of: 1- Medulla 2- Pons 3- Midbrain The medulla Contains vital centers that regulate the heart rate, blood pressure and breathing Contains integrating centers for swallowing, coughing, sneezing and vomiting Allows passage of sensory and motor tracts  The Pons Pons: Allows passage of tracts to join cerebrum with cerebellum and spinal cord Participates in control of breathing  The Midbrain Midbrain: Allows passage of tracts to join cerebrum with cerebellum and spinal cord Has connections with visual and auditory pathways  2- The Diencephalon - Found in the central part of the brain - Consists of: Thalamus Hypothalamus  Functions of the thalamus ◦Relay station for most types of sensation (except olfaction) ◦Connected with the cortex, cerebellum, and basal ganglia to control voluntary movements Hypothalamus - The hypothalamus is a diencephalon structure that is located in the lower part of the brain above the pituitary gland.  Hypothalamus - Its connection with the pituitary gland is an example of the neuro-endocrine relationship Functions of the hypothalamus ◦Controls the release of hormones from the pituitary gland ◦Controls food intake (hunger and satiety) ◦Controls water intake ◦Controls body temperature Functions of the hypothalamus ◦The higher autonomic center ◦Plays a role in the generation of emotions & behavior ◦Plays a role in sleep ◦Controls the circadian rhythm of the body  3- The Cerebrum Two hemispheres Each Consists of: ◦Cerebral cortex ◦White matter ◦Basal ganglia ◦Hippocampal formation ◦Amygdala The Cerebrum Each hemisphere is divided into: ◦Frontal lobe ◦Temporal lobe ◦Parietal lobe ◦Occipital lobe Lobes of the brain Sensory Cortex The site that receives the sensory information (discriminates modality, locality and intensity of sensations) There are two somatosensory areas: ◦Area I (postcentral gyrus) ◦Area II (wall of Sylvian Fissure) Representation of the body at the sensory cortex 1- To contralateral side 2- Upside down 3- Size reflects the number of receptors The motor cortex Known as area 4, or the he primary motor cortex (or Precentral gyrus) The site that sends orders for voluntary movements Body representation in the motor cortex Upside down Size proportional to skill of movement Can enlarge or shift (plasticity) Controls opposite side The prefrontal cortex (anterior part of the frontal lobe)  Prefrontal Cortex Functions Planning, decision-making, and goal setting. Example: Choosing between multiple options during problem-solving. Understanding social events and taking appropriate emotional responses. Example: Feeling empathy and regulating impulsive reactions in social interactions. Involves emotional regulation and individual differences. Example: Damage to the prefrontal cortex leads to significant personality changes.  Functions of basal ganglia Planning and programming of movements Initiation of voluntary movement ◦Discharge from basal ganglia and lateral parts of the cerebellum is noticed before movements start  Functions of basal ganglia Associated movements Subconscious movements (e.g., scaling of movement) Inhibition of muscle tone Posture taken to perform some voluntary movements The Limbic System The limbic system is part of the brain that is responsible for the emotional reactions. Has effects on the endocrine and autonomic systems  The Limbic System The main structures of clinical relevance: Amygdala Hippocampus Hypothalamus Plus the other structures  The Limbic System The hippocampus also converts short term memory into long term memory (= for consolidation of memory) 4- The Cerebellum  The Cerebellum Lies in the posterior fossa, posterior to the brain stem Consists of: Two hemispheres Vermis  Functions Controls rate, range and direction of voluntary movement (Coordination) Increases muscle tone (facilitator) Controls posture and balance Makes adjustments and predictions of a repeated movement (learning)