Nervous System 1 - Vertebrate Anatomy & Physiology

Welcom Nervous System 5720 – Vertebrate Anatomy & Physiology Functions of the Nervous System The nervous system has three major functions: 1. Sensory input Monitors changes both inside and outside the body e.g. sound waves (external) and blood pressure (internal). 2. Integration Proces...

Welcom Nervous System 5720 – Vertebrate Anatomy & Physiology Functions of the Nervous System The nervous system has three major functions: 1. Sensory input Monitors changes both inside and outside the body e.g. sound waves (external) and blood pressure (internal). 2. Integration Processes input and decides what to do about it. 3. Motor output Effects a response by activating the effector (muscles or glands) e.g. the heart and the pancreas. Divisions of the Nervous System Central Nervous System (CNS) - the integration and control centres, consisting of: the Brain the Spinal Cord Peripheral Nervous System (PNS) - communication lines between the CNS and the rest of the body, consisting of: Cranial Nerves Spinal Nerves Peripheral nerves Divisions of the Nervous System Peripheral System is further divided: Sensory (afferent) - conducts impulses from receptors to the CNS, Motor (efferent) - conducts impulses from the CNS to effectors, and which is further divided into: Somatic (voluntary) - to skeletal muscles Autonomic (involuntary) - to smooth and cardiac muscle and glands. Again there are two divisions: Sympathetic - “fight or flight” Parasympathetic - “resting and digesting”  Nervo us Syste m Centr Periphe al ral Nervo Nervous us System Syste m Sensor Motor y (Affere (Effere nt) nt) Somati Autonomi c c (Volunta (Involunta ry) ry) Sympathet Parasympatheti ic (Fight or c (Resting and Flight) Digesting) Neuro ns Nerve Cells These can be from 1mm – >1m long. They generate and conduct an electrical signal and only work in one direction. A neuron has 3 parts Cell body (also called Soma) Dendrites Axon Myelinati on Nerve cell processes (axons & less commonly, dendrites) may be covered by a white insulation called Myelin Made by Schwann cells who wrap themselves around the axon Speeds up impulse conduction Gaps between Schwann cells = nodes of Ranvier Node of Ranvier https://medchrome.com/extras/facts/louisantoine- ranvier-eponym-node- ranvier/ Classification of neurons Neurons are classified as: Sensory or Afferent - transmit impulses from sensory receptors to the CNS. Their cell bodies are located in sensory ganglia outside the CNS. Motor or Efferent - carry impulses away from the CNS to effector organs (muscles or glands). Most have their cell bodies within the CNS. Association - lie within the CNS between the sensory and motor neurons. 99% of neurons are association neurons. NOTE: Afferent and Efferent are very similar terms. To help remember the difference, use the acronym SAME. This links the word Sensory with Afferent, and Motor with Efferent. Sensory Receptors These are structures that respond to stimuli, which are changes in the external and internal environment. There are two types: Modified dendritic endings Mechanoreceptors - pressure, touch, stretch Thermoreceptors - heat Photoreceptors - light Chemoreceptors - taste, smell, O2 and CO2 levels Nociceptors – pain Sense Organs - eyes, ears (Coming soon to a lecture near you) Synaps es Synapses are the junctions between two neurons - generally the axons of one with the dendrites of another - or between a neuron and an effector. Two types: Electrical synapses - found in heart and smooth muscles to allow synchronized activity. Chemical synapses - where chemical neurotransmitters transfer the action potential from one neuron to the next. The impulse causes the release of the neurotransmitter from the pre-synaptic terminal to diffuse across the synaptic cleft to post-synaptic receptors in neurons or effector organs. These transmitter substances may act to excite or inhibit depending Synaptic cleft Reflex es A reflex is a rapid, predictable involuntary motor response to a stimulus. Reflexes can be somatic, which result in contraction of skeletal muscle, or autonomic, which activate involuntary muscle and glands. A reflex arc is a neural pathway consisting of 5 steps: receptor - site of stimulus sensory neuron - afferent impulses to CNS integration in CNS - may be one synapse only motor neuron - efferent impulses to effector effector - muscle or gland Reflex arc 5 step process Central Nervous System Parts of the Brain The principal parts of the brain are: Cerebral Hemispheres or Cerebrum Diencephalon (the term used to describe collectively the hypothalamus, thalamus and sometimes pituitary) Brain Stem (collectively the medulla, pons and midbrain) Cerebellum  Higher sensory Higher area intellectual area Memory Primary auditory Visual area associati Language on comprehensio n Different animal brains https://www.reddit.com/r/interestingasfuck/comments/9wtgpm/different_brains_c ompared_to_hu Comparative animal brains http://www.suzanaherculanohouz el.com/  Cerebru m Largest part of the brain Higher-order behaviours (learning, intelligence, awareness etc) Receives and interprets sensory information, initiates conscious nerve impulses to skeletal muscles, integrates neuron activity associated with communication, expression of emotional responses, learning, memory and recall Has folds (gyri) and fissures (sulci) Longitudinal fissure divides Cerebellum (little brain) Involuntary control of complex somatic motor patterns including maintenance of balance. Memory storage of learned motor patterns. Adjusts output of other somatic motor centres in brain and spinal cord i.e. the cerebrum and cerebellum work together in assessing movement, position and the need for adjustments for posture and co-ordination of movements. Diencephalon (through brain) Thalamus relay stations for all sensory impulses except smell to the cerebral cortex. relays motor impulses from the cerebral cortex to the spinal cord. interprets pain, temperature, light touch and pressure sensations. anterior nucleus functions in memory. Diencepha lon Hypothalamus centres controlling autonomic functions and hormone production from the pituitary. Pituitary Gland controls release of hypothalamic hormones secretes hormones regulating endocrine activity Brain Stem Midbrain: an area lying between the pons and the diencephalon relays motor impulses from the cerebral cortex to the pons and spinal cord, and relays sensory impulses from the spinal cord to the thalamus. processes visual and auditory data. moderates involuntary somatic motor reflexes. concerned with maintenance of consciousness. Brain Stem Anatomy Brain Stem Pons relays impulses within the brain and between parts of the brain and spinal cord contains involuntary somatic and visceral motor centres especially those related to respiration. Medulla Oblongata relays sensory impulses to thalamus. relays motor impulses from frontal lobe to spinal cord. autonomic centres for regulation of visceral (organ) function i.e. cardiovascular, respiratory and digestive system activities. area of cross over of voluntary motor Protection of the Brain and Spinal Cord Protection is provided by the bones of the skull and vertebrae, the meninges and cerebrospinal fluid (CSF), and the blood-brain barrier. Skull is made up of sections, joined together to form immovable joints (synarthrodial) with Skull sutures https://www.frontiersin.org/articles/10.3389/fcell.2021.653579/ful l Skull Fontanelles https://teachmeanatomy.info/head/osteology/skull/  Increased Intracranial Pressure The skull is an immoveable structure. When trauma happens (such as concussion) and bleeding occurs within/around the brain, there is no space for swelling to occur. This results in an increase in the pressure of the brain (intracranial) and leads to potential brain damage This is why head injuries are so CT image of haemorrhage on the brain https://www.j-stroke.org/upload/pdf/jos-2016-00 difficult to treat and need careful 563.pdf monitoring Mening es The meninges are three layers of membranes that surround the brain and the spinal cord. The outer layer - the Dura mater is tough and fibrous and has two layers with a space between containing tissue fluids, blood vessels including large sinuses. The superficial layer of the dura is fused to the periosteum of the skull. The middle layer - the Arachnoid mater is a web-like layer made up of a smooth membrane lying under the dura and web-like projections that connect to the layer below. The space between the membrane and the pia is called the subarachnoid space and this is where cerebrospinal fluid flows. The inner layer - the Pia mater is a delicate transparent membrane that is fused to the surface of the brain and spinal cord and covers the blood vessels that penetrate the brain. Meninges in brain https://www.thoughtco.com/brain-anatomy-meninges-4018883 Meninges in spinal cord https://www.verywellhealth.com/meninges-anatomy-function-conditions-5190214 Spinal Cord The spinal cord is a two way conduction cord between the brain and the rest of the body, and is also a reflex centre. Formed entirely from neurons - cell bodies, axons and dendrites - with a small amount of supporting tissue. Extends from the foramen magnum to the sixth or seventh lumbar vertebra (in the dog), although the lumbar and sacral nerves continue to travel within the vertebral canal, this collection of nerve roots being known as the cauda equina. Spinal Cord The efferent axons of the autonomic and somatic motor neurons leave the cord via the ventral root, while afferent fibres from sensory cell neurons located in ganglia on the dorsal root (dorsal root ganglia) enter the spinal cord via the dorsal root. The fusion of the dorsal and ventral roots on either side of the spinal cord forms the spinal Thank you for listenin g!