Lect2 Structure And Function Of The Nervous System PDF

Lecture 2 Structure and function of the nervous system [Chapter 2 cont’d] 30 OCTOBER 2024 1 Anatomical terminology Human terminology based on animal Dorsal: the back (dorsum in Latin) Ventral: the belly (ventrum in Latin)...

Lecture 2 Structure and function of the nervous system [Chapter 2 cont’d] 30 OCTOBER 2024 1 Anatomical terminology Human terminology based on animal Dorsal: the back (dorsum in Latin) Ventral: the belly (ventrum in Latin) Rostral: the beak (rostrum in Latin) Caudal: the tail (caudum in Latin) 2 Anatomical terminology Cross-sections (slices) of the brain Coronal (frontal): front to back (or anterior to posterior) Sagittal (longitudinal): left to right (lateral to medial to lateral again) Axial (horizontal, transverse): top to bottom (or dorsal to ventral, for the brain) 3 Anatomical terminology What you need to remember (and be able to apply): 4 The Nervous System Central Nervous System (CNS) Brain (cerebrum, cerebellum, brainstem) Spinal Cord Cluster of neurons = nucleus (nuclei) Peripheral Nervous System (PNS) Nervous system that is not the Brain + Spinal Cord Cluster of neurons = ganglion (ganglia) 5 The Nervous System – PNS Main function: to connect the CNS to the limbs and organs E.g., dorsal root ganglion: sensory neurons that transmit sensory information from the body to the central nervous system 6 The Nervous System – PNS Consists of Somatic motor system: voluntary muscles Autonomic motor system: involuntary muscles (reflexes) and organs (e.g., heart, bladder,…). This system is always active but can be in a sympathetic or parasympathetic state. Sympathetic state: expending energy (‘fight or flight’) Parasympathetic state: conserving energy (‘rest and digest’) 7 The Nervous System – PNS e.g., dorsal root ganglia 8 The Nervous System – CNS Neurons can be found in the thin sheet of tissue on the ‘outside’ of the brain (the grey matter) and in (mostly) subcortical nuclei. Neurons in distant brain areas are connected via axons with myelin sheets that form the white matter. 9 The Nervous System – CNS The CNS is covered with three protective membranes (the meninges): Dura Mater: thick membrane, closest to the skull Arachnoid Mater. Not attached to the dura mater. Does not line the brain down to the sulci (except for the longitudinal fissure). Pia Mater. Delicate membrane that firmly adheres to the surface of the brain. Can get infected (i.e., meningitis). 10 The Nervous System – CNS Your brain floats in cerebrospinal fluid (CSF): the area between the arachnoid membrane and the pia mater (i.e., the subarachnoid space) is filled with CSF. To protect the brain (e.g., reduces shock to the brain when hit on the head), and to clean it (?). 11 The Nervous System – CNS Cavities in the brain also filled with CSF: ventricles. Four large ventricles that are all connected: Left and right lateral ventricle interventricular foramen Third ventricle cerebral aqueduct Fourth ventricle 12 The Nervous System – CNS Blood supply Your brain needs energy and oxygen! This is delivered via blood (the brain consumes about 20% of your blood supply) Interruptions of blood supply to the brain (i.e., a stroke) can be caused by an obstruction of an artery or by hemorrhage from a blood vessel. This can cause damage to the brain, i.e., brain lesions 13 The Nervous System – CNS Blood supply Two main sources: Internal carotid arteries Vertebral arteries Left and right vertebral arteries merge at the level of the pons: basilar artery Basilar artery and internal carotid meet at circle of Willis 14 Structure of the CNS Basic parts: 1. Spinal cord Medulla 2. Brainstem Pons Midbrain [Cerebellum] Thalamus 3. Diencephalon Hypothalamus Limbic system 4. Telencephalon: Cerebrum Basal Ganglia Cerebral Cortex 15 Structure of the CNS: 1. Spinal Cord Spinal cord is enclosed by the bony vertebral column Vertebral column is divided into cervical, thoracic, lumbar, sacral and coccygeal regions. 16 Structure of the CNS: 1. Spinal Cord Each segment of the vertebral column gives rise to peripheral (spinal) nerves that innervate the body Sensory signal enter the spinal cord via the dorsal horn (afferent signals – towards the CNS) and leave it via the ventral horn (efferent signals – away from the CNS). Some signals go directly from the dorsal to the ventral horn, via an interneuron (e.g., spinal reflexes like the knee jerk). 17 Structure of the CNS: 2. Brainstem Highly complex structure that houses the nuclei most essential for the maintenance of life! Damage to the brainstem is very bad news… Three main parts: a. Medulla (oblongata) b. Pons + Cerebellum c. Midbrain 18 Structure of the CNS: 2. Brainstem a. Medulla (oblongata) Cell bodies of many of the 12 cranial nerves (sensory and motor innervations to face, neck, throat) Corticospinal motor axons (i.e., axons coming from the cortex to the spinal cord) cross here: motor neurons from left hemisphere cross here to control muscles from the right side of the body responsible for autonomic (involuntary) functions such as heart rate, sneezing, blood pressure, … 19 Structure of the CNS: 2. Brainstem b. Pons + Cerebellum Pons (‘bridge’): contains nuclei that connect – or bridge - the forebrain to the cerebellum, and nuclei that deal with sleep, swallowing, facial expressions and more. Also related to sleep paralysis. Cerebellum (‘little brain’): Houses ~70 billion neurons! Mostly known for its involvement in motor control and maintaining balance. More recently, also implicated in aspects of cognitive processing (e.g., language, attention). Reticular formation: Located throughout the brainstem. Crucially involved in arousal and attention. Damage to the reticular formation is likely to affect the state of consciousness (i.e., results in coma) Home to the raphe nuclei (serotonin synthesis) 20 Structure of the CNS: 2. Brainstem c. Midbrain (mesencephalon) Dorsal part: the tectum Houses superior and inferior colliculi that are involved in reflections towards visual and auditory stimuli, respectively Ventral part: the tegmentum Houses the Ventral Tegmental Area and Substantia Nigra where dopamine is produced Periaqueductal Grey: modulation of pain signals 21 Structure of the CNS: 3. Diencephalon a. Thalamus and b. Hypothalamus 22 Structure of the CNS: 3. Diencephalon a. Thalamus Left and right thalamus, connected via the Massa Intermedia Switch board of the brain. Receives input from all sensory areas of the brain (except smell) Consists of several nuclei that act as specific relays for incoming sensory information: Lateral geniculate nucleus: visual information Medial geniculate nucleus: auditory information Ventral posterior nuclei: somatosensory information Pulvinar: attention and integrative functions 23 Structure of the CNS: 3. Diencephalon b. Hypothalamus Controls the functions necessary for homeostasis (i.e., the normal state of the body): ✓ Body temperature ✓ Metabolic rate ✓ Circadian rhythm ✓ … Produces hormones but also regulates hormone production in other areas, for example in the pituitary gland (axonal connections to the posterior pituitary gland). 24 Structure of the CNS Basic parts: 1. Spinal cord Medulla 2. Brainstem Pons Midbrain [Cerebellum] Thalamus 3. Diencephalon Hypothalamus Limbic system 4. Telencephalon: Cerebrum Basal Ganglia Cerebral Cortex 25 Structure of the CNS: 4. Telencephalon (Cerebrum) a. Limbic system b. Basal Ganglia (chapter 8) Cingulate cortex (Anterior CC in chapter 12) Striatum: Putamen + Caudate nucleus Hippocampus: critical for memory, spatial Globus Pallidus processing (see Chapter 8) Nucleus Accumbens Amygdala: emotional processing (see Chapter 10) c. Olfactory bulbs: Processing of olfactory information (smell) d. Cerebral Cortex (!!) 26 The Cerebral Cortex Cortex is thin folded sheet of neurons and supporting cells Folding creates convex convolutions (gyri) and concavities between the gyri (sulci) E.g., central sulcus is dividing concavity between frontal and parietal lobe. The gyrus anterior of the central sulcus is the precentral gyrus; the gyrus posterior of the central sulcus is the postcentral gyrus). 27 The Cerebral Cortex Each hemisphere has 4 main divisions Frontal lobe Parietal lobe Occipital lobe Temporal lobe 28 The Cerebral Cortex More subdivisions: according to microanatomy (cytoarchitectonics) Korbinian Brodmann: 52 different areas (Brodmann Areas; BA) Lateral view Medial view A little bit outdated. Brain activity with modern neuroimaging tools does not overlap neatly with BA’s 29 The Cerebral Cortex Most of the neocortex consist of 6 cellular layers (laminae). This is often called the grey matter. Evolutionary older parts of the brain have less layers (e.g., paleocortex, archicortex). 30 The Cerebral Cortex Layers differ in cell densities, cell types, inputs, and outputs 1: no cell bodies, mostly axons and dendrites 2-3: pyramidal cells, locally connected to other cortical sites 4: stellate cells, receive input from thalamus 5-6: large pyramidal cells, output leaves the cortex Arranged in a vertical structures called cortical columns of about 0.5 mm wide. 31 The Cerebral Cortex: Functional division Caution: Mapping cognitive functions to specific brain areas is debatable! Fusiform Face Area is not only involved in face perception. Generally, functionally divided in 5 subtypes: Primary sensory areas (chapter 5) Primary motor areas (chapter 8) Unimodal association areas (processing only one type of information) Multimodal association areas (integrating more than one type of information) Paralimbic and limbic areas (see limbic system) 32 The Cerebral Cortex: Functional division The Frontal lobe Motor cortex: in front of central sulcus Primary motor cortex (generating movements) Premotor cortex (controlling movements) Supplemental motor cortex (planning movements) Prefrontal cortex: anterior to the motor cortex Houses executive functions (chapter 12): planning, organizing, controlling and executing behavior. Last to develop (!!); evolutionary the youngest 33 The Cerebral Cortex: Functional division The Parietal lobe Somatosensory cortex: the postcentral sulcus Primary somatosensory cortex (S1): receives input from thalamus. Info about touch, pain, temperature, limb position. Secondary somatosensory cortex (S2): unimodal association area that further processes sensory information) 34 The Cerebral Cortex: Functional division The Occipital lobe The Temporal lobe Visual cortex Auditory cortex 35 The Human Brain Primates have a higher ratio of neuron number to brain size Off all primates, humans have the largest brains 36 The Human Brain Connectivity according to “small-world” architecture (chapter 4): Local ‘modules’ with short connections Small number of very long connections Structural connectivity relates to functional connectivity In language processing, Wernicke’s area (related to interpreting an auditory code) is strongly connected to distant Broca’s area (related to speech production) via a dense bundle of axons, the Arcuate Fasciculus. Image obtained with diffusion tensor imaging (DTI; see chapter 3) 37 The Human Brain Overview of early development (p. 63 – p.66) can be skipped. The size of the brain quadruples from birth to adulthood. Not because of an increase in neurons, but because of synaptogenesis (the formation of synapses) and the growth of dendritic trees, the extension of axons, myelination and the proliferation of glial cells. Synaptogenesis is followed by synaptic pruning (i.e., eliminating redundant synaptic connections). Use it or lose it! Maturation of the cortex can be indicated by gray matter volume loss 38 The Human brain So, when we mature, white matter increases linearly with age, but gray matter first increases and then decreases. The maturation of gray matter differs depending on the cortical region. Less mature More mature From Gogtay et al. (2004) 39 Next Lecture (4th November): Methods of Cognitive Neuroscience 40